From 3d9a5ae4ec0ec1871b8aeb13b0de2ff7ee616179 Mon Sep 17 00:00:00 2001
From: szager-chromium <szager@chromium.org>
Date: Thu, 27 Jun 2024 18:35:46 +0000
Subject: [PATCH] Merge pull request #523 from szager-chromium/v2-pr

SHA: 027e2ddb4da9eda1ddd0605d9b2dbf10c0ede260
Reason: push, by szager-chromium

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
---
 index.html | 1864 +++++++++++++++++++++++++++++++++++-----------------
 1 file changed, 1270 insertions(+), 594 deletions(-)

diff --git a/index.html b/index.html
index b6cbf5a..18752f8 100644
--- a/index.html
+++ b/index.html
@@ -5,9 +5,11 @@
   <title>Intersection Observer</title>
   <meta content="ED" name="w3c-status">
   <link href="https://www.w3.org/StyleSheets/TR/2021/W3C-ED" rel="stylesheet">
-  <meta content="Bikeshed version 82ce88815, updated Thu Sep 7 16:33:55 2023 -0700" name="generator">
+  <meta content="Bikeshed version a1dabb26c, updated Mon Jun 17 15:00:44 2024 -0700" name="generator">
   <link href="https://www.w3.org/TR/intersection-observer/" rel="canonical">
-  <meta content="ef83cd25ec091f25420a0b487c23210b64c9cfff" name="document-revision">
+  <meta content="027e2ddb4da9eda1ddd0605d9b2dbf10c0ede260" name="revision">
+  <meta content="dark light" name="color-scheme">
+  <link href="https://www.w3.org/StyleSheets/TR/2021/dark.css" media="(prefers-color-scheme: dark)" rel="stylesheet" type="text/css">
 <style>/* Boilerplate: style-autolinks */
 .css.css, .property.property, .descriptor.descriptor {
     color: var(--a-normal-text);
@@ -79,7 +81,6 @@
 }
 </style>
 <style>/* Boilerplate: style-colors */
-
 /* Any --*-text not paired with a --*-bg is assumed to have a transparent bg */
 :root {
     color-scheme: light dark;
@@ -333,11 +334,15 @@
 :root {
     --dfnpanel-bg: #ddd;
     --dfnpanel-text: var(--text);
+    --dfnpanel-target-bg: #ffc;
+    --dfnpanel-target-outline: orange;
 }
 @media (prefers-color-scheme: dark) {
     :root {
         --dfnpanel-bg: #222;
         --dfnpanel-text: var(--text);
+        --dfnpanel-target-bg: #333;
+        --dfnpanel-target-outline: silver;
     }
 }
 .dfn-panel {
@@ -360,11 +365,13 @@
 .dfn-panel > b { display: block; }
 .dfn-panel a { color: var(--dfnpanel-text); }
 .dfn-panel a:not(:hover) { text-decoration: none !important; border-bottom: none !important; }
+.dfn-panel a:focus {
+    outline: 5px auto Highlight;
+    outline: 5px auto -webkit-focus-ring-color;
+}
 .dfn-panel > b + b { margin-top: 0.25em; }
 .dfn-panel ul { padding: 0 0 0 1em; list-style: none; }
 .dfn-panel li a {
-    white-space: pre;
-    display: inline-block;
     max-width: calc(300px - 1.5em - 1em);
     overflow: hidden;
     text-overflow: ellipsis;
@@ -373,67 +380,84 @@
 .dfn-panel.activated {
     display: inline-block;
     position: fixed;
-    left: .5em;
+    left: 8px;
     bottom: 2em;
     margin: 0 auto;
     max-width: calc(100vw - 1.5em - .4em - .5em);
     max-height: 30vh;
+    transition: left 1s ease-out, bottom 1s ease-out;
 }
 
-.dfn-paneled[role="button"] { cursor: pointer; }
-</style>
-<style>/* Boilerplate: style-dfn-panel */
-:root {
-    --dfnpanel-bg: #ddd;
-    --dfnpanel-text: var(--text);
+.dfn-panel .link-item:hover {
+    text-decoration: underline;
 }
-@media (prefers-color-scheme: dark) {
-    :root {
-        --dfnpanel-bg: #222;
-        --dfnpanel-text: var(--text);
-    }
+.dfn-panel .link-item .copy-icon {
+    opacity: 0;
 }
-.dfn-panel {
-    position: absolute;
-    z-index: 35;
-    width: 20em;
-    width: 300px;
-    height: auto;
-    max-height: 500px;
-    overflow: auto;
-    padding: 0.5em 0.75em;
-    font: small Helvetica Neue, sans-serif, Droid Sans Fallback;
-    background: var(--dfnpanel-bg);
-    color: var(--dfnpanel-text);
-    border: outset 0.2em;
-    white-space: normal; /* in case it's moved into a pre */
+.dfn-panel .link-item:hover .copy-icon,
+.dfn-panel .link-item .copy-icon:focus {
+    opacity: 1;
 }
-.dfn-panel:not(.on) { display: none; }
-.dfn-panel * { margin: 0; padding: 0; text-indent: 0; }
-.dfn-panel > b { display: block; }
-.dfn-panel a { color: var(--dfnpanel-text); }
-.dfn-panel a:not(:hover) { text-decoration: none !important; border-bottom: none !important; }
-.dfn-panel > b + b { margin-top: 0.25em; }
-.dfn-panel ul { padding: 0 0 0 1em; list-style: none; }
-.dfn-panel li a {
-    white-space: pre;
+
+.dfn-panel .copy-icon {
     display: inline-block;
-    max-width: calc(300px - 1.5em - 1em);
-    overflow: hidden;
-    text-overflow: ellipsis;
+    margin-right: 0.5em;
+    width: 0.85em;
+    height: 1em;
+    border-radius: 3px;
+    background-color: #ccc;
+    cursor: pointer;
+}
+
+.dfn-panel .copy-icon .icon {
+    width: 100%;
+    height: 100%;
+    background-color: #fff;
+    display: flex;
+    justify-content: center;
+    align-items: center;
+    position: relative;
 }
 
-.dfn-panel.activated {
-    display: inline-block;
-    position: fixed;
-    left: .5em;
-    bottom: 2em;
-    margin: 0 auto;
-    max-width: calc(100vw - 1.5em - .4em - .5em);
-    max-height: 30vh;
+.dfn-panel .copy-icon .icon::before {
+    content: "";
+    position: absolute;
+    top: 0;
+    left: 0;
+    width: 100%;
+    height: 100%;
+    border: 1px solid black;
+    background-color: #ccc;
+    opacity: 0.25;
+    transform: translate(3px, -3px);
 }
 
-.dfn-paneled[role="button"] { cursor: pointer; }
+.dfn-panel .copy-icon:active .icon::before {
+    opacity: 1;
+}
+
+.dfn-paneled[role="button"] { cursor: help; }
+
+.highlighted {
+    animation: target-fade 3s;
+}
+
+@keyframes target-fade {
+    from {
+        background-color: var(--dfnpanel-target-bg);
+        outline: 5px solid var(--dfnpanel-target-outline);
+    }
+    to {
+        color: var(--a-normal-text);
+        background-color: transparent;
+        outline: transparent;
+    }
+}
+</style>
+<style>/* Boilerplate: style-idl-highlighting */
+pre.idl.highlight {
+    background: var(--borderedblock-bg, var(--def-bg));
+}
 </style>
 <style>/* Boilerplate: style-issues */
 a[href].issue-return {
@@ -459,12 +483,16 @@
 	--mdn-bg: #EEE;
 	--mdn-shadow: #999;
 	--mdn-nosupport-text: #ccc;
+	--mdn-pass: green;
+	--mdn-fail: red;
 }
 @media (prefers-color-scheme: dark) {
 	:root {
 		--mdn-bg: #222;
 		--mdn-shadow: #444;
 		--mdn-nosupport-text: #666;
+		--mdn-pass: #690;
+		--mdn-fail: #d22;
 	}
 }
 .mdn-anno {
@@ -507,11 +535,11 @@
 	display: block;
 }
 .mdn-anno > summary > .less-than-two-engines-flag {
-	color: red;
+	color: var(--mdn-fail);
 	padding-right: 2px;
 }
 .mdn-anno > summary > .all-engines-flag {
-	color: green;
+	color: var(--mdn-pass);
 	padding-right: 2px;
 }
 .mdn-anno > summary > span {
@@ -532,10 +560,10 @@
 	padding-top: 2px;
 }
 .mdn-anno > .feature > .less-than-two-engines-text {
-	color: red;
+	color: var(--mdn-fail);
 }
 .mdn-anno > .feature > .all-engines-text {
-	color: green;
+	color: var(--mdn-pass);
 }
 .mdn-anno > .feature > p {
 	font-size: .75em;
@@ -674,8 +702,40 @@
 	margin: -40px 0 0 0;
 }
 </style>
-<style>/* Boilerplate: style-selflinks */
+<style>/* Boilerplate: style-ref-hints */
+:root {
+    --ref-hint-bg: #ddd;
+    --ref-hint-text: var(--text);
+}
+@media (prefers-color-scheme: dark) {
+    :root {
+        --ref-hint-bg: #222;
+        --ref-hint-text: var(--text);
+    }
+}
 
+.ref-hint {
+    display: inline-block;
+    position: absolute;
+    z-index: 35;
+    width: 20em;
+    width: 300px;
+    height: auto;
+    max-height: 500px;
+    overflow: auto;
+    padding: 0.5em 0.5em;
+    font: small Helvetica Neue, sans-serif, Droid Sans Fallback;
+    background: var(--ref-hint-bg);
+    color: var(--ref-hint-text);
+    border: outset 0.2em;
+    white-space: normal; /* in case it's moved into a pre */
+}
+
+.ref-hint * { margin: 0; padding: 0; text-indent: 0; }
+
+.ref-hint ul { padding: 0 0 0 1em; list-style: none; }
+</style>
+<style>/* Boilerplate: style-selflinks */
 :root {
     --selflink-text: white;
     --selflink-bg: gray;
@@ -735,14 +795,6 @@
 dfn > a.self-link::before      { content: "#"; }
 </style>
 <style>/* Boilerplate: style-syntax-highlighting */
-
-            pre.idl.highlight {
-                background: var(--borderedblock-bg, var(--def-bg));
-            }
-            
-</style>
-<style>/* Boilerplate: style-syntax-highlighting */
-
 code.highlight { padding: .1em; border-radius: .3em; }
 pre.highlight, pre > code.highlight { display: block; padding: 1em; margin: .5em 0; overflow: auto; border-radius: 0; }
 
@@ -800,7 +852,6 @@
 c-[vi] { color: #0077aa } /* Name.Variable.Instance */
 c-[il] { color: #000000 } /* Literal.Number.Integer.Long */
 
-
 @media (prefers-color-scheme: dark) {
     .highlight:not(.idl) { background: rgba(255, 255, 255, .05); }
 
@@ -868,7 +919,7 @@
   <div class="head">
    <p data-fill-with="logo"><a class="logo" href="https://www.w3.org/"> <img alt="W3C" height="48" src="https://www.w3.org/StyleSheets/TR/2021/logos/W3C" width="72"> </a> </p>
    <h1 class="p-name no-ref" id="title">Intersection Observer</h1>
-   <p id="w3c-state"><a href="https://www.w3.org/standards/types#ED">Editor’s Draft</a>, <time class="dt-updated" datetime="2023-10-18">18 October 2023</time></p>
+   <p id="w3c-state"><a href="https://www.w3.org/standards/types#ED">Editor’s Draft</a>, <time class="dt-updated" datetime="2024-06-27">27 June 2024</time></p>
    <details open>
     <summary>More details about this document</summary>
     <div data-fill-with="spec-metadata">
@@ -878,7 +929,7 @@ <h1 class="p-name no-ref" id="title">Intersection Observer</h1>
       <dt>Latest published version:
       <dd><a href="https://www.w3.org/TR/intersection-observer/">https://www.w3.org/TR/intersection-observer/</a>
       <dt>Previous Versions:
-      <dd><a href="https://www.w3.org/TR/2023/WD-intersection-observer-20231003/" rel="prev">https://www.w3.org/TR/2023/WD-intersection-observer-20231003/</a>
+      <dd><a href="https://www.w3.org/TR/2023/WD-intersection-observer-20231018/" rel="prev">https://www.w3.org/TR/2023/WD-intersection-observer-20231018/</a>
       <dt>Test Suite:
       <dd><a href="http://w3c-test.org/intersection-observer/">http://w3c-test.org/intersection-observer/</a>
       <dt>Feedback:
@@ -893,7 +944,7 @@ <h1 class="p-name no-ref" id="title">Intersection Observer</h1>
     </div>
    </details>
    <div data-fill-with="warning"></div>
-   <p class="copyright" data-fill-with="copyright"><a href="https://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a> © 2023 <a href="https://www.w3.org/">World Wide Web Consortium</a>. <abbr title="World Wide Web Consortium">W3C</abbr><sup>®</sup> <a href="https://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>, <a href="https://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a> and <a href="https://www.w3.org/Consortium/Legal/copyright-software" rel="license" title="W3C Software and Document License">permissive document license</a> rules apply. </p>
+   <p class="copyright" data-fill-with="copyright"><a href="https://www.w3.org/policies/#copyright">Copyright</a> © 2024 <a href="https://www.w3.org/">World Wide Web Consortium</a>. <abbr title="World Wide Web Consortium">W3C</abbr><sup>®</sup> <a href="https://www.w3.org/policies/#Legal_Disclaimer">liability</a>, <a href="https://www.w3.org/policies/#W3C_Trademarks">trademark</a> and <a href="https://www.w3.org/copyright/software-license/" rel="license" title="W3C Software and Document License">permissive document license</a> rules apply. </p>
    <hr title="Separator for header">
   </div>
   <div class="p-summary" data-fill-with="abstract">
@@ -911,8 +962,8 @@ <h2 class="no-num no-toc no-ref heading settled" id="sotd"><span class="content"
    <p> Publication as an Editors Draft does not imply endorsement by <abbr title="World Wide Web Consortium">W3C</abbr> and its Members. This is a draft document and may
     be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite
     this document as other than work in progress. </p>
-   <p> This document was produced by a group operating under the <a href="https://www.w3.org/Consortium/Patent-Policy-20200915/"><abbr title="World Wide Web Consortium">W3C</abbr> Patent Policy</a>. <abbr title="World Wide Web Consortium">W3C</abbr> maintains a <a href="https://www.w3.org/2004/01/pp-impl/114929/status" rel="disclosure">public list of any patent disclosures</a> made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains <a href="https://www.w3.org/Consortium/Patent-Policy-20200915/#def-essential">Essential Claim(s)</a> must disclose the information in accordance with <a href="https://www.w3.org/Consortium/Patent-Policy-20200915/#sec-Disclosure">section 6 of the <abbr title="World Wide Web Consortium">W3C</abbr> Patent Policy</a>. </p>
-   <p>This document is governed by the <a href="https://www.w3.org/2023/Process-20230612/" id="w3c_process_revision">12 June 2023 W3C Process Document</a>. </p>
+   <p> This document was produced by a group operating under the <a href="https://www.w3.org/policies/patent-policy/20200915/"><abbr title="World Wide Web Consortium">W3C</abbr> Patent Policy</a>. <abbr title="World Wide Web Consortium">W3C</abbr> maintains a <a href="https://www.w3.org/2004/01/pp-impl/114929/status" rel="disclosure">public list of any patent disclosures</a> made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains <a href="https://www.w3.org/policies/patent-policy/20200915/#def-essential">Essential Claim(s)</a> must disclose the information in accordance with <a href="https://www.w3.org/policies/patent-policy/20200915/#sec-Disclosure">section 6 of the <abbr title="World Wide Web Consortium">W3C</abbr> Patent Policy</a>. </p>
+   <p>This document is governed by the <a href="https://www.w3.org/policies/process/20231103/" id="w3c_process_revision">03 November 2023 W3C Process Document</a>. </p>
   </div>
   <div data-fill-with="at-risk"></div>
   <nav data-fill-with="table-of-contents" id="toc">
@@ -947,7 +998,9 @@ <h2 class="no-num no-toc no-ref" id="contents">Table of Contents</h2>
         <li><a href="#notify-intersection-observers-algo"><span class="secno">3.2.5</span> <span class="content"> Notify Intersection Observers</span></a>
         <li><a href="#queue-intersection-observer-entry-algo"><span class="secno">3.2.6</span> <span class="content"> Queue an IntersectionObserverEntry</span></a>
         <li><a href="#calculate-intersection-rect-algo"><span class="secno">3.2.7</span> <span class="content"> Compute the Intersection of a Target Element and the Root</span></a>
-        <li><a href="#update-intersection-observations-algo"><span class="secno">3.2.8</span> <span class="content"> Run the Update Intersection Observations Steps</span></a>
+        <li><a href="#calculate-visibility-algo"><span class="secno">3.2.8</span> <span class="content"> Compute whether a Target is unoccluded, untransformed, unfiltered, and opaque.</span></a>
+        <li><a href="#calculate-effective-transformation-matrix"><span class="secno">3.2.9</span> <span class="content">Calculate a <span>target</span>’s Effective Transformation Matrix</span></a>
+        <li><a href="#update-intersection-observations-algo"><span class="secno">3.2.10</span> <span class="content"> Run the Update Intersection Observations Steps</span></a>
        </ol>
       <li><a href="#lifetime"><span class="secno">3.3</span> <span class="content"> IntersectionObserver Lifetime</span></a>
       <li>
@@ -1061,9 +1114,9 @@ <h2 class="heading settled" data-level="2" id="intersection-observer-api"><span
 visibility and position of <dfn class="dfn-paneled" data-dfn-for="IntersectionObserver" data-dfn-type="dfn" data-noexport id="intersectionobserver-target">target</dfn> DOM
 elements relative to an <a data-link-type="dfn" href="#intersectionobserver-intersection-root" id="ref-for-intersectionobserver-intersection-root">intersection root</a>.</p>
    <h3 class="heading settled" data-level="2.1" id="intersection-observer-callback"><span class="secno">2.1. </span><span class="content"> The IntersectionObserverCallback</span><a class="self-link" href="#intersection-observer-callback"></a></h3>
-<pre class="idl highlight def"><c- b>callback</c-> <dfn class="dfn-paneled idl-code" data-dfn-type="callback" data-export id="callbackdef-intersectionobservercallback"><code><c- g>IntersectionObserverCallback</c-></code></dfn> = <a class="idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-undefined" id="ref-for-idl-undefined"><c- b>undefined</c-></a> (<a data-link-type="dfn" href="https://webidl.spec.whatwg.org/#idl-sequence" id="ref-for-idl-sequence"><c- b>sequence</c-></a>&lt;<a data-link-type="idl-name" href="#intersectionobserverentry" id="ref-for-intersectionobserverentry"><c- n>IntersectionObserverEntry</c-></a>> <dfn class="idl-code" data-dfn-for="IntersectionObserverCallback" data-dfn-type="argument" data-export id="dom-intersectionobservercallback-entries"><code><c- g>entries</c-></code><a class="self-link" href="#dom-intersectionobservercallback-entries"></a></dfn>, <a data-link-type="idl-name" href="#intersectionobserver" id="ref-for-intersectionobserver"><c- n>IntersectionObserver</c-></a> <dfn class="idl-code" data-dfn-for="IntersectionObserverCallback" data-dfn-type="argument" data-export id="dom-intersectionobservercallback-observer"><code><c- g>observer</c-></code><a class="self-link" href="#dom-intersectionobservercallback-observer"></a></dfn>);
+<pre class="idl highlight def"><c- b>callback</c-> <dfn class="dfn-paneled idl-code" data-dfn-type="callback" data-export id="callbackdef-intersectionobservercallback"><code><c- g>IntersectionObserverCallback</c-></code></dfn> = <a class="idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-undefined" id="ref-for-idl-undefined"><c- b>undefined</c-></a> (<a data-link-type="dfn" href="https://webidl.spec.whatwg.org/#idl-sequence" id="ref-for-idl-sequence"><c- b>sequence</c-></a>&lt;<a data-link-type="idl-name" href="#intersectionobserverentry" id="ref-for-intersectionobserverentry"><c- n>IntersectionObserverEntry</c-></a>> <dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserverCallback" data-dfn-type="argument" data-export id="dom-intersectionobservercallback-entries"><code><c- g>entries</c-></code></dfn>, <a data-link-type="idl-name" href="#intersectionobserver" id="ref-for-intersectionobserver"><c- n>IntersectionObserver</c-></a> <dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserverCallback" data-dfn-type="argument" data-export id="dom-intersectionobservercallback-observer"><code><c- g>observer</c-></code></dfn>);
 </pre>
-   <p>This callback will be invoked when there are changes to <a data-link-type="dfn" href="#intersectionobserver-target" id="ref-for-intersectionobserver-target">target</a>’s
+   <p>This callback will be invoked when there are changes to a <a data-link-type="dfn" href="#intersectionobserver-target" id="ref-for-intersectionobserver-target">target</a>’s
 intersection with the <a data-link-type="dfn" href="#intersectionobserver-intersection-root" id="ref-for-intersectionobserver-intersection-root①">intersection root</a>, as per the <a data-link-type="dfn" href="#intersection-observer-processing-model" id="ref-for-intersection-observer-processing-model">processing model</a>.</p>
    <h3 class="heading settled" data-level="2.2" id="intersection-observer-interface"><span class="secno">2.2. </span><span class="content"> The IntersectionObserver interface</span><a class="self-link" href="#intersection-observer-interface"></a></h3>
    <p>The <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver①">IntersectionObserver</a></code> interface can be used to observe changes in the
@@ -1075,7 +1128,7 @@ <h3 class="heading settled" data-level="2.2" id="intersection-observer-interface
    <p>An <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver③">IntersectionObserver</a></code> with a non-<code>null</code> <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-root" id="ref-for-dom-intersectionobserver-root①">root</a></code> is referred to as an <dfn class="dfn-paneled" data-dfn-for="IntersectionObserver" data-dfn-type="dfn" data-noexport id="intersectionobserver-explicit-root-observer">explicit root observer</dfn>,
 and it can observe any <a data-link-type="dfn" href="#intersectionobserver-target" id="ref-for-intersectionobserver-target②">target</a> <code class="idl"><a data-link-type="idl" href="https://dom.spec.whatwg.org/#element" id="ref-for-element①">Element</a></code> that is a descendant of the <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-root" id="ref-for-dom-intersectionobserver-root②">root</a></code> in the <a data-link-type="dfn" href="https://drafts.csswg.org/css-display/#containing-block-chain" id="ref-for-containing-block-chain">containing block chain</a>.
 An <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver④">IntersectionObserver</a></code> with a <code>null</code> <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-root" id="ref-for-dom-intersectionobserver-root③">root</a></code> is referred to as an <dfn class="dfn-paneled" data-dfn-for="IntersectionObserver" data-dfn-type="dfn" data-noexport id="intersectionobserver-implicit-root-observer">implicit root observer</dfn>.
-Valid <a data-link-type="dfn" href="#intersectionobserver-target" id="ref-for-intersectionobserver-target③">targets</a> for an <a data-link-type="dfn" href="#intersectionobserver-implicit-root-observer" id="ref-for-intersectionobserver-implicit-root-observer">implicit root observer</a> include
+Valid <a data-link-type="dfn" href="#intersectionobserver-target" id="ref-for-intersectionobserver-target③">target</a>s for an <a data-link-type="dfn" href="#intersectionobserver-implicit-root-observer" id="ref-for-intersectionobserver-implicit-root-observer">implicit root observer</a> include
 any <code class="idl"><a data-link-type="idl" href="https://dom.spec.whatwg.org/#element" id="ref-for-element②">Element</a></code> in the <a data-link-type="dfn" href="https://html.spec.whatwg.org/multipage/browsers.html#top-level-browsing-context" id="ref-for-top-level-browsing-context①">top-level browsing context</a>,
 as well as any <code class="idl"><a data-link-type="idl" href="https://dom.spec.whatwg.org/#element" id="ref-for-element③">Element</a></code> in any <a data-link-type="dfn" href="https://html.spec.whatwg.org/multipage/browsers.html#nested-browsing-context" id="ref-for-nested-browsing-context">nested browsing context</a> which is in the <a data-link-type="dfn" href="https://html.spec.whatwg.org/multipage/browsers.html#list-of-the-descendant-browsing-contexts" id="ref-for-list-of-the-descendant-browsing-contexts">list of the descendant browsing contexts</a> of the <a data-link-type="dfn" href="https://html.spec.whatwg.org/multipage/browsers.html#top-level-browsing-context" id="ref-for-top-level-browsing-context②">top-level browsing context</a>.</p>
    <p>When dealing with <a data-link-type="dfn" href="#intersectionobserver-implicit-root-observer" id="ref-for-intersectionobserver-implicit-root-observer①">implicit root observers</a>, the API makes a distinction between
@@ -1091,20 +1144,22 @@ <h3 class="heading settled" data-level="2.2" id="intersection-observer-interface
 use-cases. Per-<code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-observe" id="ref-for-dom-intersectionobserver-observe">observe()</a></code> options could be provided in the future if the need arises.</p>
 <pre class="idl highlight def">[<a class="idl-code" data-link-type="extended-attribute" href="https://webidl.spec.whatwg.org/#Exposed" id="ref-for-Exposed"><c- g>Exposed</c-></a>=<c- n>Window</c->]
 <c- b>interface</c-> <dfn class="dfn-paneled idl-code" data-dfn-type="interface" data-export id="intersectionobserver"><code><c- g>IntersectionObserver</c-></code></dfn> {
-  <dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserver" data-dfn-type="constructor" data-export data-lt="IntersectionObserver(callback, options)|constructor(callback, options)|IntersectionObserver(callback)|constructor(callback)" id="dom-intersectionobserver-intersectionobserver"><code><c- g>constructor</c-></code></dfn>(<a data-link-type="idl-name" href="#callbackdef-intersectionobservercallback" id="ref-for-callbackdef-intersectionobservercallback"><c- n>IntersectionObserverCallback</c-></a> <dfn class="idl-code" data-dfn-for="IntersectionObserver/IntersectionObserver(callback, options), IntersectionObserver/constructor(callback, options), IntersectionObserver/IntersectionObserver(callback), IntersectionObserver/constructor(callback)" data-dfn-type="argument" data-export id="dom-intersectionobserver-intersectionobserver-callback-options-callback"><code><c- g>callback</c-></code><a class="self-link" href="#dom-intersectionobserver-intersectionobserver-callback-options-callback"></a></dfn>, <c- b>optional</c-> <a data-link-type="idl-name" href="#dictdef-intersectionobserverinit" id="ref-for-dictdef-intersectionobserverinit"><c- n>IntersectionObserverInit</c-></a> <dfn class="idl-code" data-dfn-for="IntersectionObserver/IntersectionObserver(callback, options), IntersectionObserver/constructor(callback, options), IntersectionObserver/IntersectionObserver(callback), IntersectionObserver/constructor(callback)" data-dfn-type="argument" data-export id="dom-intersectionobserver-intersectionobserver-callback-options-options"><code><c- g>options</c-></code><a class="self-link" href="#dom-intersectionobserver-intersectionobserver-callback-options-options"></a></dfn> = {});
+  <dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserver" data-dfn-type="constructor" data-export data-lt="IntersectionObserver(callback, options)|constructor(callback, options)|IntersectionObserver(callback)|constructor(callback)" id="dom-intersectionobserver-intersectionobserver"><code><c- g>constructor</c-></code></dfn>(<a data-link-type="idl-name" href="#callbackdef-intersectionobservercallback" id="ref-for-callbackdef-intersectionobservercallback"><c- n>IntersectionObserverCallback</c-></a> <dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserver/IntersectionObserver(callback, options), IntersectionObserver/constructor(callback, options), IntersectionObserver/IntersectionObserver(callback), IntersectionObserver/constructor(callback)" data-dfn-type="argument" data-export id="dom-intersectionobserver-intersectionobserver-callback-options-callback"><code><c- g>callback</c-></code></dfn>, <c- b>optional</c-> <a data-link-type="idl-name" href="#dictdef-intersectionobserverinit" id="ref-for-dictdef-intersectionobserverinit"><c- n>IntersectionObserverInit</c-></a> <dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserver/IntersectionObserver(callback, options), IntersectionObserver/constructor(callback, options), IntersectionObserver/IntersectionObserver(callback), IntersectionObserver/constructor(callback)" data-dfn-type="argument" data-export id="dom-intersectionobserver-intersectionobserver-callback-options-options"><code><c- g>options</c-></code></dfn> = {});
   <c- b>readonly</c-> <c- b>attribute</c-> (<a data-link-type="idl-name" href="https://dom.spec.whatwg.org/#element" id="ref-for-element④"><c- n>Element</c-></a> <c- b>or</c-> <a data-link-type="idl-name" href="https://dom.spec.whatwg.org/#document" id="ref-for-document①"><c- n>Document</c-></a>)? <a class="idl-code" data-link-type="attribute" data-readonly data-type="(Element or Document)?" href="#dom-intersectionobserver-root" id="ref-for-dom-intersectionobserver-root④"><c- g>root</c-></a>;
   <c- b>readonly</c-> <c- b>attribute</c-> <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-DOMString" id="ref-for-idl-DOMString"><c- b>DOMString</c-></a> <a class="idl-code" data-link-type="attribute" data-readonly data-type="DOMString" href="#dom-intersectionobserver-rootmargin" id="ref-for-dom-intersectionobserver-rootmargin"><c- g>rootMargin</c-></a>;
   <c- b>readonly</c-> <c- b>attribute</c-> <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-DOMString" id="ref-for-idl-DOMString①"><c- b>DOMString</c-></a> <a class="idl-code" data-link-type="attribute" data-readonly data-type="DOMString" href="#dom-intersectionobserver-scrollmargin" id="ref-for-dom-intersectionobserver-scrollmargin"><c- g>scrollMargin</c-></a>;
   <c- b>readonly</c-> <c- b>attribute</c-> <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-frozen-array" id="ref-for-idl-frozen-array"><c- b>FrozenArray</c-></a>&lt;<a class="idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-double" id="ref-for-idl-double"><c- b>double</c-></a>> <a class="idl-code" data-link-type="attribute" data-readonly data-type="FrozenArray<double>" href="#dom-intersectionobserver-thresholds" id="ref-for-dom-intersectionobserver-thresholds"><c- g>thresholds</c-></a>;
-  <a class="idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-undefined" id="ref-for-idl-undefined①"><c- b>undefined</c-></a> <a class="idl-code" data-link-type="method" href="#dom-intersectionobserver-observe" id="ref-for-dom-intersectionobserver-observe①"><c- g>observe</c-></a>(<a data-link-type="idl-name" href="https://dom.spec.whatwg.org/#element" id="ref-for-element⑤"><c- n>Element</c-></a> <dfn class="idl-code" data-dfn-for="IntersectionObserver/observe(target)" data-dfn-type="argument" data-export id="dom-intersectionobserver-observe-target-target"><code><c- g>target</c-></code><a class="self-link" href="#dom-intersectionobserver-observe-target-target"></a></dfn>);
-  <a class="idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-undefined" id="ref-for-idl-undefined②"><c- b>undefined</c-></a> <a class="idl-code" data-link-type="method" href="#dom-intersectionobserver-unobserve" id="ref-for-dom-intersectionobserver-unobserve"><c- g>unobserve</c-></a>(<a data-link-type="idl-name" href="https://dom.spec.whatwg.org/#element" id="ref-for-element⑥"><c- n>Element</c-></a> <dfn class="idl-code" data-dfn-for="IntersectionObserver/unobserve(target)" data-dfn-type="argument" data-export id="dom-intersectionobserver-unobserve-target-target"><code><c- g>target</c-></code><a class="self-link" href="#dom-intersectionobserver-unobserve-target-target"></a></dfn>);
+  <c- b>readonly</c-> <c- b>attribute</c-> <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-long" id="ref-for-idl-long"><c- b>long</c-></a> <a class="idl-code" data-link-type="attribute" data-readonly data-type="long" href="#dom-intersectionobserver-delay" id="ref-for-dom-intersectionobserver-delay"><c- g>delay</c-></a>;
+  <c- b>readonly</c-> <c- b>attribute</c-> <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-boolean" id="ref-for-idl-boolean"><c- b>boolean</c-></a> <a class="idl-code" data-link-type="attribute" data-readonly data-type="boolean" href="#dom-intersectionobserver-trackvisibility" id="ref-for-dom-intersectionobserver-trackvisibility"><c- g>trackVisibility</c-></a>;
+  <a class="idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-undefined" id="ref-for-idl-undefined①"><c- b>undefined</c-></a> <a class="idl-code" data-link-type="method" href="#dom-intersectionobserver-observe" id="ref-for-dom-intersectionobserver-observe①"><c- g>observe</c-></a>(<a data-link-type="idl-name" href="https://dom.spec.whatwg.org/#element" id="ref-for-element⑤"><c- n>Element</c-></a> <dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserver/observe(target)" data-dfn-type="argument" data-export id="dom-intersectionobserver-observe-target-target"><code><c- g>target</c-></code></dfn>);
+  <a class="idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-undefined" id="ref-for-idl-undefined②"><c- b>undefined</c-></a> <a class="idl-code" data-link-type="method" href="#dom-intersectionobserver-unobserve" id="ref-for-dom-intersectionobserver-unobserve"><c- g>unobserve</c-></a>(<a data-link-type="idl-name" href="https://dom.spec.whatwg.org/#element" id="ref-for-element⑥"><c- n>Element</c-></a> <dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserver/unobserve(target)" data-dfn-type="argument" data-export id="dom-intersectionobserver-unobserve-target-target"><code><c- g>target</c-></code></dfn>);
   <a class="idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-undefined" id="ref-for-idl-undefined③"><c- b>undefined</c-></a> <a class="idl-code" data-link-type="method" href="#dom-intersectionobserver-disconnect" id="ref-for-dom-intersectionobserver-disconnect"><c- g>disconnect</c-></a>();
   <a data-link-type="dfn" href="https://webidl.spec.whatwg.org/#idl-sequence" id="ref-for-idl-sequence①"><c- b>sequence</c-></a>&lt;<a data-link-type="idl-name" href="#intersectionobserverentry" id="ref-for-intersectionobserverentry①"><c- n>IntersectionObserverEntry</c-></a>> <a class="idl-code" data-link-type="method" href="#dom-intersectionobserver-takerecords" id="ref-for-dom-intersectionobserver-takerecords"><c- g>takeRecords</c-></a>();
 };
 </pre>
    <div>
     <dl>
-     <dt data-md><dfn class="idl-code" data-dfn-for="IntersectionObserver" data-dfn-type="constructor" data-export data-lt="IntersectionObserver(callback, options = {})" id="dom-intersectionobserver-intersectionobserver-callback-options"><code> new IntersectionObserver(callback, options)</code><a class="self-link" href="#dom-intersectionobserver-intersectionobserver-callback-options"></a></dfn>
+     <dt data-md><dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserver" data-dfn-type="constructor" data-export data-lt="IntersectionObserver(callback, options = {})" id="dom-intersectionobserver-intersectionobserver-callback-options"><code> new IntersectionObserver(callback, options)</code></dfn>
      <dd data-md>
       <p>Return the result of running the <a data-link-type="dfn" href="#initialize-a-new-intersectionobserver" id="ref-for-initialize-a-new-intersectionobserver">initialize a new IntersectionObserver</a> algorithm, providing <var>callback</var> and <var>options</var>.</p>
      <dt data-md><dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserver" data-dfn-type="method" data-export id="dom-intersectionobserver-observe"><code>observe(target)</code></dfn>
@@ -1115,7 +1170,7 @@ <h3 class="heading settled" data-level="2.2" id="intersection-observer-interface
       <p>Run the <a data-link-type="dfn" href="#unobserve-a-target-element" id="ref-for-unobserve-a-target-element">unobserve a target Element</a> algorithm, providing <var>this</var> and <var>target</var>.</p>
       <p class="note" role="note"><span class="marker">Note:</span> <code class="idl"><a data-link-type="idl" href="https://dom.spec.whatwg.org/#mutationobserver" id="ref-for-mutationobserver①">MutationObserver</a></code> does not implement <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-unobserve" id="ref-for-dom-intersectionobserver-unobserve①">unobserve()</a></code>.
 For <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver⑦">IntersectionObserver</a></code>, <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-unobserve" id="ref-for-dom-intersectionobserver-unobserve②">unobserve()</a></code> addresses the
-lazy-loading use case. After <var>target</var> becomes visible,
+lazy-loading use case. After loading is initiated for <var>target</var>,
 it does not need to be tracked.
 It would be more work to either <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-disconnect" id="ref-for-dom-intersectionobserver-disconnect①">disconnect()</a></code> all <var>target</var>s
 and <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-observe" id="ref-for-dom-intersectionobserver-observe②">observe()</a></code> the remaining ones,
@@ -1170,12 +1225,20 @@ <h3 class="heading settled" data-level="2.2" id="intersection-observer-interface
 of the thresholds are crossed for that target.
 If no <var>options</var>.<code class="idl"><a data-link-type="idl" href="#dom-intersectionobserverinit-threshold" id="ref-for-dom-intersectionobserverinit-threshold①">threshold</a></code> was provided to the <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver①④">IntersectionObserver</a></code> constructor, or the sequence is empty, the value
 of this attribute will be [0].</p>
+     <dt data-md><dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserver" data-dfn-type="attribute" data-export id="dom-intersectionobserver-delay"><code>delay</code></dfn>, <span> of type <a data-link-type="idl-name" href="https://webidl.spec.whatwg.org/#idl-long" id="ref-for-idl-long①">long</a>, readonly</span>
+     <dd data-md>
+      <p>A number indicating the minimum delay in milliseconds
+between notifications from this observer for a given target.</p>
+     <dt data-md><dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserver" data-dfn-type="attribute" data-export id="dom-intersectionobserver-trackvisibility"><code>trackVisibility</code></dfn>, <span> of type <a data-link-type="idl-name" href="https://webidl.spec.whatwg.org/#idl-boolean" id="ref-for-idl-boolean①">boolean</a>, readonly</span>
+     <dd data-md>
+      <p>A boolean indicating whether this <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver①⑤">IntersectionObserver</a></code> will track
+changes in a target’s <a data-link-type="dfn" href="#visibility" id="ref-for-visibility">visibility</a>.</p>
     </dl>
    </div>
    <p>An <code class="idl"><a data-link-type="idl" href="https://dom.spec.whatwg.org/#element" id="ref-for-element⑦">Element</a></code> is defined as having a <dfn class="dfn-paneled" data-dfn-for="IntersectionObserver" data-dfn-type="dfn" data-noexport id="intersectionobserver-content-clip">content clip</dfn> if its computed style has <a data-link-type="dfn" href="https://drafts.csswg.org/css-overflow-3/#overflow-properties" id="ref-for-overflow-properties">overflow properties</a> that cause its content to be clipped to the element’s <a data-link-type="dfn" href="https://drafts.csswg.org/css-box/#padding-edge" id="ref-for-padding-edge">padding edge</a>.</p>
-   <p>The <dfn class="dfn-paneled" data-dfn-for="IntersectionObserver" data-dfn-type="dfn" data-noexport id="intersectionobserver-root-intersection-rectangle">root intersection rectangle</dfn> for an <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver①⑤">IntersectionObserver</a></code> is the rectangle we’ll use to check against the targets.</p>
+   <p>The <dfn class="dfn-paneled" data-dfn-for="IntersectionObserver" data-dfn-type="dfn" data-noexport id="intersectionobserver-root-intersection-rectangle">root intersection rectangle</dfn> for an <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver①⑥">IntersectionObserver</a></code> is the rectangle we’ll use to check against the targets.</p>
    <dl class="switch">
-    <dt>If the <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver①⑥">IntersectionObserver</a></code> is an <a data-link-type="dfn" href="#intersectionobserver-implicit-root-observer" id="ref-for-intersectionobserver-implicit-root-observer②">implicit root observer</a>, 
+    <dt>If the <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver①⑦">IntersectionObserver</a></code> is an <a data-link-type="dfn" href="#intersectionobserver-implicit-root-observer" id="ref-for-intersectionobserver-implicit-root-observer②">implicit root observer</a>, 
     <dd>it’s treated as if the root were the <a data-link-type="dfn" href="https://html.spec.whatwg.org/multipage/browsers.html#top-level-browsing-context" id="ref-for-top-level-browsing-context③">top-level browsing context</a>’s <code class="idl"><a data-link-type="idl" href="https://html.spec.whatwg.org/multipage/nav-history-apis.html#dom-document-2" id="ref-for-dom-document-2①">document</a></code>, according to the following rule for <code class="idl"><a data-link-type="idl" href="https://html.spec.whatwg.org/multipage/nav-history-apis.html#dom-document-2" id="ref-for-dom-document-2②">document</a></code>. 
     <dt>If the <a data-link-type="dfn" href="#intersectionobserver-intersection-root" id="ref-for-intersectionobserver-intersection-root⑤">intersection root</a> is a <code class="idl"><a data-link-type="idl" href="https://html.spec.whatwg.org/multipage/nav-history-apis.html#dom-document-2" id="ref-for-dom-document-2③">document</a></code>, 
     <dd>it’s the size of the <code class="idl"><a data-link-type="idl" href="https://html.spec.whatwg.org/multipage/nav-history-apis.html#dom-document-2" id="ref-for-dom-document-2④">document</a></code>'s <a data-link-type="dfn" href="https://drafts.csswg.org/css2/visuren.html#viewport" id="ref-for-viewport②">viewport</a> (note that this processing step can only be reached if the <code class="idl"><a data-link-type="idl" href="https://html.spec.whatwg.org/multipage/nav-history-apis.html#dom-document-2" id="ref-for-dom-document-2⑤">document</a></code> is <a data-link-type="dfn" href="https://html.spec.whatwg.org/multipage/browsers.html#fully-active" id="ref-for-fully-active">fully active</a>). 
@@ -1186,7 +1249,7 @@ <h3 class="heading settled" data-level="2.2" id="intersection-observer-interface
    </dl>
    <p>When calculating the <a data-link-type="dfn" href="#intersectionobserver-root-intersection-rectangle" id="ref-for-intersectionobserver-root-intersection-rectangle①">root intersection rectangle</a> for
 a <a data-link-type="dfn" href="#intersectionobserver-same-origin-domain-target" id="ref-for-intersectionobserver-same-origin-domain-target②">same-origin-domain target</a>, the rectangle is then expanded
-according to the offsets in the <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver①⑦">IntersectionObserver</a></code>’s <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-rootmargin-slot" id="ref-for-dom-intersectionobserver-rootmargin-slot①">[[rootMargin]]</a></code> slot
+according to the offsets in the <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver①⑧">IntersectionObserver</a></code>’s <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-rootmargin-slot" id="ref-for-dom-intersectionobserver-rootmargin-slot①">[[rootMargin]]</a></code> slot
 in a manner similar to CSS’s <a class="property css" data-link-type="property" href="https://drafts.csswg.org/css-box-4/#propdef-margin" id="ref-for-propdef-margin">margin</a> property,
 with the four values indicating the amount the top, right, bottom, and left edges, respectively, are offset by,
 with positive lengths indicating an outward offset.
@@ -1198,7 +1261,7 @@ <h3 class="heading settled" data-level="2.2" id="intersection-observer-interface
     <dd data-md>
      <p>When calculating a <a data-link-type="dfn" href="https://drafts.csswg.org/css-overflow-3/#scrollport" id="ref-for-scrollport①">scrollport</a> intersection rectangle for
 a <a data-link-type="dfn" href="#intersectionobserver-same-origin-domain-target" id="ref-for-intersectionobserver-same-origin-domain-target③">same-origin-domain target</a>, the rectangle is expanded
-according to the offsets in the <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver①⑧">IntersectionObserver</a></code>’s <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-scrollmargin-slot" id="ref-for-dom-intersectionobserver-scrollmargin-slot①">[[scrollMargin]]</a></code> slot
+according to the offsets in the <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver①⑨">IntersectionObserver</a></code>’s <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-scrollmargin-slot" id="ref-for-dom-intersectionobserver-scrollmargin-slot①">[[scrollMargin]]</a></code> slot
 in a manner similar to CSS’s <a class="property css" data-link-type="property" href="https://drafts.csswg.org/css-box-4/#propdef-margin" id="ref-for-propdef-margin①">margin</a> property,
 with the four values indicating the amount the top, right, bottom, and left edges, respectively, are offset by,
 with positive lengths indicating an outward offset.
@@ -1251,24 +1314,26 @@ <h3 class="heading settled" data-level="2.2" id="intersection-observer-interface
    <h3 class="heading settled" data-level="2.3" id="intersection-observer-entry"><span class="secno">2.3. </span><span class="content"> The IntersectionObserverEntry interface</span><a class="self-link" href="#intersection-observer-entry"></a></h3>
 <pre class="idl highlight def">[<a class="idl-code" data-link-type="extended-attribute" href="https://webidl.spec.whatwg.org/#Exposed" id="ref-for-Exposed①"><c- g>Exposed</c-></a>=<c- n>Window</c->]
 <c- b>interface</c-> <dfn class="dfn-paneled idl-code" data-dfn-type="interface" data-export id="intersectionobserverentry"><code><c- g>IntersectionObserverEntry</c-></code></dfn> {
-  <dfn class="idl-code" data-dfn-for="IntersectionObserverEntry" data-dfn-type="constructor" data-export data-lt="IntersectionObserverEntry(intersectionObserverEntryInit)|constructor(intersectionObserverEntryInit)" id="dom-intersectionobserverentry-intersectionobserverentry"><code><c- g>constructor</c-></code><a class="self-link" href="#dom-intersectionobserverentry-intersectionobserverentry"></a></dfn>(<a data-link-type="idl-name" href="#dictdef-intersectionobserverentryinit" id="ref-for-dictdef-intersectionobserverentryinit"><c- n>IntersectionObserverEntryInit</c-></a> <dfn class="idl-code" data-dfn-for="IntersectionObserverEntry/IntersectionObserverEntry(intersectionObserverEntryInit), IntersectionObserverEntry/constructor(intersectionObserverEntryInit)" data-dfn-type="argument" data-export id="dom-intersectionobserverentry-intersectionobserverentry-intersectionobserverentryinit-intersectionobserverentryinit"><code><c- g>intersectionObserverEntryInit</c-></code><a class="self-link" href="#dom-intersectionobserverentry-intersectionobserverentry-intersectionobserverentryinit-intersectionobserverentryinit"></a></dfn>);
+  <dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserverEntry" data-dfn-type="constructor" data-export data-lt="IntersectionObserverEntry(intersectionObserverEntryInit)|constructor(intersectionObserverEntryInit)" id="dom-intersectionobserverentry-intersectionobserverentry"><code><c- g>constructor</c-></code></dfn>(<a data-link-type="idl-name" href="#dictdef-intersectionobserverentryinit" id="ref-for-dictdef-intersectionobserverentryinit"><c- n>IntersectionObserverEntryInit</c-></a> <dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserverEntry/IntersectionObserverEntry(intersectionObserverEntryInit), IntersectionObserverEntry/constructor(intersectionObserverEntryInit)" data-dfn-type="argument" data-export id="dom-intersectionobserverentry-intersectionobserverentry-intersectionobserverentryinit-intersectionobserverentryinit"><code><c- g>intersectionObserverEntryInit</c-></code></dfn>);
   <c- b>readonly</c-> <c- b>attribute</c-> <a data-link-type="idl-name" href="http://www.w3.org/TR/hr-time/#domhighrestimestamp" id="ref-for-domhighrestimestamp"><c- n>DOMHighResTimeStamp</c-></a> <a class="idl-code" data-link-type="attribute" data-readonly data-type="DOMHighResTimeStamp" href="#dom-intersectionobserverentry-time" id="ref-for-dom-intersectionobserverentry-time"><c- g>time</c-></a>;
   <c- b>readonly</c-> <c- b>attribute</c-> <a data-link-type="idl-name" href="https://drafts.fxtf.org/geometry-1/#domrectreadonly" id="ref-for-domrectreadonly"><c- n>DOMRectReadOnly</c-></a>? <a class="idl-code" data-link-type="attribute" data-readonly data-type="DOMRectReadOnly?" href="#dom-intersectionobserverentry-rootbounds" id="ref-for-dom-intersectionobserverentry-rootbounds"><c- g>rootBounds</c-></a>;
   <c- b>readonly</c-> <c- b>attribute</c-> <a data-link-type="idl-name" href="https://drafts.fxtf.org/geometry-1/#domrectreadonly" id="ref-for-domrectreadonly①"><c- n>DOMRectReadOnly</c-></a> <a class="idl-code" data-link-type="attribute" data-readonly data-type="DOMRectReadOnly" href="#dom-intersectionobserverentry-boundingclientrect" id="ref-for-dom-intersectionobserverentry-boundingclientrect"><c- g>boundingClientRect</c-></a>;
   <c- b>readonly</c-> <c- b>attribute</c-> <a data-link-type="idl-name" href="https://drafts.fxtf.org/geometry-1/#domrectreadonly" id="ref-for-domrectreadonly②"><c- n>DOMRectReadOnly</c-></a> <a class="idl-code" data-link-type="attribute" data-readonly data-type="DOMRectReadOnly" href="#dom-intersectionobserverentry-intersectionrect" id="ref-for-dom-intersectionobserverentry-intersectionrect"><c- g>intersectionRect</c-></a>;
-  <c- b>readonly</c-> <c- b>attribute</c-> <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-boolean" id="ref-for-idl-boolean"><c- b>boolean</c-></a> <a class="idl-code" data-link-type="attribute" data-readonly data-type="boolean" href="#dom-intersectionobserverentry-isintersecting" id="ref-for-dom-intersectionobserverentry-isintersecting"><c- g>isIntersecting</c-></a>;
+  <c- b>readonly</c-> <c- b>attribute</c-> <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-boolean" id="ref-for-idl-boolean②"><c- b>boolean</c-></a> <a class="idl-code" data-link-type="attribute" data-readonly data-type="boolean" href="#dom-intersectionobserverentry-isintersecting" id="ref-for-dom-intersectionobserverentry-isintersecting"><c- g>isIntersecting</c-></a>;
+  <c- b>readonly</c-> <c- b>attribute</c-> <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-boolean" id="ref-for-idl-boolean③"><c- b>boolean</c-></a> <a class="idl-code" data-link-type="attribute" data-readonly data-type="boolean" href="#dom-intersectionobserverentry-isvisible" id="ref-for-dom-intersectionobserverentry-isvisible"><c- g>isVisible</c-></a>;
   <c- b>readonly</c-> <c- b>attribute</c-> <a class="idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-double" id="ref-for-idl-double②"><c- b>double</c-></a> <a class="idl-code" data-link-type="attribute" data-readonly data-type="double" href="#dom-intersectionobserverentry-intersectionratio" id="ref-for-dom-intersectionobserverentry-intersectionratio"><c- g>intersectionRatio</c-></a>;
   <c- b>readonly</c-> <c- b>attribute</c-> <a data-link-type="idl-name" href="https://dom.spec.whatwg.org/#element" id="ref-for-element⑨"><c- n>Element</c-></a> <a class="idl-code" data-link-type="attribute" data-readonly data-type="Element" href="#dom-intersectionobserverentry-target" id="ref-for-dom-intersectionobserverentry-target"><c- g>target</c-></a>;
 };
 
 <c- b>dictionary</c-> <dfn class="dfn-paneled idl-code" data-dfn-type="dictionary" data-export id="dictdef-intersectionobserverentryinit"><code><c- g>IntersectionObserverEntryInit</c-></code></dfn> {
-  <c- b>required</c-> <a data-link-type="idl-name" href="http://www.w3.org/TR/hr-time/#domhighrestimestamp" id="ref-for-domhighrestimestamp①"><c- n>DOMHighResTimeStamp</c-></a> <dfn class="idl-code" data-dfn-for="IntersectionObserverEntryInit" data-dfn-type="dict-member" data-export data-type="DOMHighResTimeStamp " id="dom-intersectionobserverentryinit-time"><code><c- g>time</c-></code><a class="self-link" href="#dom-intersectionobserverentryinit-time"></a></dfn>;
-  <c- b>required</c-> <a data-link-type="idl-name" href="https://drafts.fxtf.org/geometry-1/#dictdef-domrectinit" id="ref-for-dictdef-domrectinit"><c- n>DOMRectInit</c-></a>? <dfn class="idl-code" data-dfn-for="IntersectionObserverEntryInit" data-dfn-type="dict-member" data-export data-type="DOMRectInit? " id="dom-intersectionobserverentryinit-rootbounds"><code><c- g>rootBounds</c-></code><a class="self-link" href="#dom-intersectionobserverentryinit-rootbounds"></a></dfn>;
-  <c- b>required</c-> <a data-link-type="idl-name" href="https://drafts.fxtf.org/geometry-1/#dictdef-domrectinit" id="ref-for-dictdef-domrectinit①"><c- n>DOMRectInit</c-></a> <dfn class="idl-code" data-dfn-for="IntersectionObserverEntryInit" data-dfn-type="dict-member" data-export data-type="DOMRectInit " id="dom-intersectionobserverentryinit-boundingclientrect"><code><c- g>boundingClientRect</c-></code><a class="self-link" href="#dom-intersectionobserverentryinit-boundingclientrect"></a></dfn>;
-  <c- b>required</c-> <a data-link-type="idl-name" href="https://drafts.fxtf.org/geometry-1/#dictdef-domrectinit" id="ref-for-dictdef-domrectinit②"><c- n>DOMRectInit</c-></a> <dfn class="idl-code" data-dfn-for="IntersectionObserverEntryInit" data-dfn-type="dict-member" data-export data-type="DOMRectInit " id="dom-intersectionobserverentryinit-intersectionrect"><code><c- g>intersectionRect</c-></code><a class="self-link" href="#dom-intersectionobserverentryinit-intersectionrect"></a></dfn>;
-  <c- b>required</c-> <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-boolean" id="ref-for-idl-boolean①"><c- b>boolean</c-></a> <dfn class="idl-code" data-dfn-for="IntersectionObserverEntryInit" data-dfn-type="dict-member" data-export data-type="boolean " id="dom-intersectionobserverentryinit-isintersecting"><code><c- g>isIntersecting</c-></code><a class="self-link" href="#dom-intersectionobserverentryinit-isintersecting"></a></dfn>;
-  <c- b>required</c-> <a class="idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-double" id="ref-for-idl-double③"><c- b>double</c-></a> <dfn class="idl-code" data-dfn-for="IntersectionObserverEntryInit" data-dfn-type="dict-member" data-export data-type="double " id="dom-intersectionobserverentryinit-intersectionratio"><code><c- g>intersectionRatio</c-></code><a class="self-link" href="#dom-intersectionobserverentryinit-intersectionratio"></a></dfn>;
-  <c- b>required</c-> <a data-link-type="idl-name" href="https://dom.spec.whatwg.org/#element" id="ref-for-element①⓪"><c- n>Element</c-></a> <dfn class="idl-code" data-dfn-for="IntersectionObserverEntryInit" data-dfn-type="dict-member" data-export data-type="Element " id="dom-intersectionobserverentryinit-target"><code><c- g>target</c-></code><a class="self-link" href="#dom-intersectionobserverentryinit-target"></a></dfn>;
+  <c- b>required</c-> <a data-link-type="idl-name" href="http://www.w3.org/TR/hr-time/#domhighrestimestamp" id="ref-for-domhighrestimestamp①"><c- n>DOMHighResTimeStamp</c-></a> <dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserverEntryInit" data-dfn-type="dict-member" data-export data-type="DOMHighResTimeStamp" id="dom-intersectionobserverentryinit-time"><code><c- g>time</c-></code></dfn>;
+  <c- b>required</c-> <a data-link-type="idl-name" href="https://drafts.fxtf.org/geometry-1/#dictdef-domrectinit" id="ref-for-dictdef-domrectinit"><c- n>DOMRectInit</c-></a>? <dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserverEntryInit" data-dfn-type="dict-member" data-export data-type="DOMRectInit?" id="dom-intersectionobserverentryinit-rootbounds"><code><c- g>rootBounds</c-></code></dfn>;
+  <c- b>required</c-> <a data-link-type="idl-name" href="https://drafts.fxtf.org/geometry-1/#dictdef-domrectinit" id="ref-for-dictdef-domrectinit①"><c- n>DOMRectInit</c-></a> <dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserverEntryInit" data-dfn-type="dict-member" data-export data-type="DOMRectInit" id="dom-intersectionobserverentryinit-boundingclientrect"><code><c- g>boundingClientRect</c-></code></dfn>;
+  <c- b>required</c-> <a data-link-type="idl-name" href="https://drafts.fxtf.org/geometry-1/#dictdef-domrectinit" id="ref-for-dictdef-domrectinit②"><c- n>DOMRectInit</c-></a> <dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserverEntryInit" data-dfn-type="dict-member" data-export data-type="DOMRectInit" id="dom-intersectionobserverentryinit-intersectionrect"><code><c- g>intersectionRect</c-></code></dfn>;
+  <c- b>required</c-> <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-boolean" id="ref-for-idl-boolean④"><c- b>boolean</c-></a> <dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserverEntryInit" data-dfn-type="dict-member" data-export data-type="boolean" id="dom-intersectionobserverentryinit-isintersecting"><code><c- g>isIntersecting</c-></code></dfn>;
+  <c- b>required</c-> <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-boolean" id="ref-for-idl-boolean⑤"><c- b>boolean</c-></a> <dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserverEntryInit" data-dfn-type="dict-member" data-export data-type="boolean" id="dom-intersectionobserverentryinit-isvisible"><code><c- g>isVisible</c-></code></dfn>;
+  <c- b>required</c-> <a class="idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-double" id="ref-for-idl-double③"><c- b>double</c-></a> <dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserverEntryInit" data-dfn-type="dict-member" data-export data-type="double" id="dom-intersectionobserverentryinit-intersectionratio"><code><c- g>intersectionRatio</c-></code></dfn>;
+  <c- b>required</c-> <a data-link-type="idl-name" href="https://dom.spec.whatwg.org/#element" id="ref-for-element①⓪"><c- n>Element</c-></a> <dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserverEntryInit" data-dfn-type="dict-member" data-export data-type="Element" id="dom-intersectionobserverentryinit-target"><code><c- g>target</c-></code></dfn>;
 };
 </pre>
    <div>
@@ -1282,15 +1347,19 @@ <h3 class="heading settled" data-level="2.3" id="intersection-observer-entry"><s
 each of <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserverentry-target" id="ref-for-dom-intersectionobserverentry-target②">target</a></code>'s ancestors' clip
 rects (up to but not including <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-root" id="ref-for-dom-intersectionobserver-root⑤">root</a></code>),
 intersected with the <a data-link-type="dfn" href="#intersectionobserver-root-intersection-rectangle" id="ref-for-intersectionobserver-root-intersection-rectangle③">root intersection rectangle</a>.
-This value represents the portion of <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserverentry-target" id="ref-for-dom-intersectionobserverentry-target③">target</a></code> actually visible
-within the <a data-link-type="dfn" href="#intersectionobserver-root-intersection-rectangle" id="ref-for-intersectionobserver-root-intersection-rectangle④">root intersection rectangle</a>.</p>
-     <dt data-md><dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserverEntry" data-dfn-type="attribute" data-export id="dom-intersectionobserverentry-isintersecting"><code>isIntersecting</code></dfn>, <span> of type <a data-link-type="idl-name" href="https://webidl.spec.whatwg.org/#idl-boolean" id="ref-for-idl-boolean②">boolean</a>, readonly</span>
+This value represents the portion of <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserverentry-target" id="ref-for-dom-intersectionobserverentry-target③">target</a></code> that intersects with
+the <a data-link-type="dfn" href="#intersectionobserver-root-intersection-rectangle" id="ref-for-intersectionobserver-root-intersection-rectangle④">root intersection rectangle</a>.</p>
+     <dt data-md><dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserverEntry" data-dfn-type="attribute" data-export id="dom-intersectionobserverentry-isintersecting"><code>isIntersecting</code></dfn>, <span> of type <a data-link-type="idl-name" href="https://webidl.spec.whatwg.org/#idl-boolean" id="ref-for-idl-boolean⑥">boolean</a>, readonly</span>
      <dd data-md>
       <p>True if the <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserverentry-target" id="ref-for-dom-intersectionobserverentry-target④">target</a></code> intersects with the <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-root" id="ref-for-dom-intersectionobserver-root⑥">root</a></code>; false otherwise.  This flag makes it
 possible to distinguish between an <code class="idl"><a data-link-type="idl" href="#intersectionobserverentry" id="ref-for-intersectionobserverentry②">IntersectionObserverEntry</a></code> signalling
 the transition from intersecting to not-intersecting; and an <code class="idl"><a data-link-type="idl" href="#intersectionobserverentry" id="ref-for-intersectionobserverentry③">IntersectionObserverEntry</a></code> signalling a transition from not-intersecting
 to intersecting with a zero-area intersection rect (as will happen with
 edge-adjacent intersections, or when the <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserverentry-boundingclientrect" id="ref-for-dom-intersectionobserverentry-boundingclientrect②">boundingClientRect</a></code> has zero area).</p>
+     <dt data-md><dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserverEntry" data-dfn-type="attribute" data-export id="dom-intersectionobserverentry-isvisible"><code>isVisible</code></dfn>, <span> of type <a data-link-type="idl-name" href="https://webidl.spec.whatwg.org/#idl-boolean" id="ref-for-idl-boolean⑦">boolean</a>, readonly</span>
+     <dd data-md>
+      <p>Contains the result of running the <a data-link-type="dfn" href="#visibility" id="ref-for-visibility①">visibility</a> algorithm
+on <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserverentry-target" id="ref-for-dom-intersectionobserverentry-target⑤">target</a></code>.</p>
      <dt data-md><dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserverEntry" data-dfn-type="attribute" data-export id="dom-intersectionobserverentry-intersectionratio"><code>intersectionRatio</code></dfn>, <span> of type <a data-link-type="idl-name" href="https://heycam.github.io/webidl/#idl-double" id="ref-for-idl-double④">double</a>, readonly</span>
      <dd data-md>
       <p>If the <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserverentry-boundingclientrect" id="ref-for-dom-intersectionobserverentry-boundingclientrect③">boundingClientRect</a></code> has non-zero area,
@@ -1314,17 +1383,19 @@ <h3 class="heading settled" data-level="2.3" id="intersection-observer-entry"><s
    </div>
    <h3 class="heading settled" data-level="2.4" id="intersection-observer-init"><span class="secno">2.4. </span><span class="content"> The IntersectionObserverInit dictionary</span><a class="self-link" href="#intersection-observer-init"></a></h3>
 <pre class="idl highlight def"><c- b>dictionary</c-> <dfn class="dfn-paneled idl-code" data-dfn-type="dictionary" data-export id="dictdef-intersectionobserverinit"><code><c- g>IntersectionObserverInit</c-></code></dfn> {
-  (<a data-link-type="idl-name" href="https://dom.spec.whatwg.org/#element" id="ref-for-element①③"><c- n>Element</c-></a> <c- b>or</c-> <a data-link-type="idl-name" href="https://dom.spec.whatwg.org/#document" id="ref-for-document②"><c- n>Document</c-></a>)?  <a class="idl-code" data-default="null" data-link-type="dict-member" data-type="(Element or Document)?  " href="#dom-intersectionobserverinit-root" id="ref-for-dom-intersectionobserverinit-root①"><c- g>root</c-></a> = <c- b>null</c->;
-  <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-DOMString" id="ref-for-idl-DOMString④"><c- b>DOMString</c-></a> <a class="idl-code" data-default="&quot;0px&quot;" data-link-type="dict-member" data-type="DOMString " href="#dom-intersectionobserverinit-rootmargin" id="ref-for-dom-intersectionobserverinit-rootmargin③"><c- g>rootMargin</c-></a> = "0px";
-  <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-DOMString" id="ref-for-idl-DOMString⑤"><c- b>DOMString</c-></a> <a class="idl-code" data-default="&quot;0px&quot;" data-link-type="dict-member" data-type="DOMString " href="#dom-intersectionobserverinit-scrollmargin" id="ref-for-dom-intersectionobserverinit-scrollmargin②"><c- g>scrollMargin</c-></a> = "0px";
-  (<a class="idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-double" id="ref-for-idl-double⑤"><c- b>double</c-></a> <c- b>or</c-> <a data-link-type="dfn" href="https://webidl.spec.whatwg.org/#idl-sequence" id="ref-for-idl-sequence②"><c- b>sequence</c-></a>&lt;<a class="idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-double" id="ref-for-idl-double⑥"><c- b>double</c-></a>>) <a class="idl-code" data-default="0" data-link-type="dict-member" data-type="(double or sequence<double>) " href="#dom-intersectionobserverinit-threshold" id="ref-for-dom-intersectionobserverinit-threshold②"><c- g>threshold</c-></a> = 0;
+  (<a data-link-type="idl-name" href="https://dom.spec.whatwg.org/#element" id="ref-for-element①③"><c- n>Element</c-></a> <c- b>or</c-> <a data-link-type="idl-name" href="https://dom.spec.whatwg.org/#document" id="ref-for-document②"><c- n>Document</c-></a>)?  <a class="idl-code" data-default="null" data-link-type="dict-member" data-type="(Element or Document)?" href="#dom-intersectionobserverinit-root" id="ref-for-dom-intersectionobserverinit-root①"><c- g>root</c-></a> = <c- b>null</c->;
+  <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-DOMString" id="ref-for-idl-DOMString④"><c- b>DOMString</c-></a> <a class="idl-code" data-default="&quot;0px&quot;" data-link-type="dict-member" data-type="DOMString" href="#dom-intersectionobserverinit-rootmargin" id="ref-for-dom-intersectionobserverinit-rootmargin③"><c- g>rootMargin</c-></a> = "0px";
+  <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-DOMString" id="ref-for-idl-DOMString⑤"><c- b>DOMString</c-></a> <a class="idl-code" data-default="&quot;0px&quot;" data-link-type="dict-member" data-type="DOMString" href="#dom-intersectionobserverinit-scrollmargin" id="ref-for-dom-intersectionobserverinit-scrollmargin②"><c- g>scrollMargin</c-></a> = "0px";
+  (<a class="idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-double" id="ref-for-idl-double⑤"><c- b>double</c-></a> <c- b>or</c-> <a data-link-type="dfn" href="https://webidl.spec.whatwg.org/#idl-sequence" id="ref-for-idl-sequence②"><c- b>sequence</c-></a>&lt;<a class="idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-double" id="ref-for-idl-double⑥"><c- b>double</c-></a>>) <a class="idl-code" data-default="0" data-link-type="dict-member" data-type="(double or sequence<double>)" href="#dom-intersectionobserverinit-threshold" id="ref-for-dom-intersectionobserverinit-threshold②"><c- g>threshold</c-></a> = 0;
+  <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-long" id="ref-for-idl-long②"><c- b>long</c-></a> <a class="idl-code" data-default="0" data-link-type="dict-member" data-type="long" href="#dom-intersectionobserverinit-delay" id="ref-for-dom-intersectionobserverinit-delay"><c- g>delay</c-></a> = 0;
+  <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-boolean" id="ref-for-idl-boolean⑧"><c- b>boolean</c-></a> <a class="idl-code" data-default="false" data-link-type="dict-member" data-type="boolean" href="#dom-intersectionobserverinit-trackvisibility" id="ref-for-dom-intersectionobserverinit-trackvisibility"><c- g>trackVisibility</c-></a> = <c- b>false</c->;
 };
 </pre>
    <div>
     <dl>
      <dt data-md><dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserverInit" data-dfn-type="dict-member" data-export id="dom-intersectionobserverinit-root"><code>root</code></dfn>, <span> of type <code class="idl-code">(Element or Document)</code>, nullable, defaulting to <code>null</code></span>
      <dd data-md>
-      <p>The <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver①⑨">root</a></code> to use for intersection.
+      <p>The <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver②⓪">root</a></code> to use for intersection.
 If not provided, use the <a data-link-type="dfn" href="#intersectionobserver-implicit-root" id="ref-for-intersectionobserver-implicit-root">implicit root</a>.</p>
      <dt data-md><dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserverInit" data-dfn-type="dict-member" data-export id="dom-intersectionobserverinit-rootmargin"><code>rootMargin</code></dfn>, <span> of type <a data-link-type="idl-name" href="https://webidl.spec.whatwg.org/#idl-DOMString" id="ref-for-idl-DOMString⑥">DOMString</a>, defaulting to <code>"0px"</code></span>
      <dd data-md>
@@ -1352,6 +1423,16 @@ <h3 class="heading settled" data-level="2.4" id="intersection-observer-init"><sp
 percentage of the area of the rectangle produced
 by <a data-link-type="dfn" href="https://drafts.csswg.org/cssom-view-1/#element-get-the-bounding-box" id="ref-for-element-get-the-bounding-box②">getting the bounding box</a> for <a data-link-type="dfn" href="#intersectionobserver-target" id="ref-for-intersectionobserver-target①①">target</a>.</p>
       <p class="note" role="note"><span class="marker">Note:</span> 0.0 is effectively "any non-zero number of pixels".</p>
+     <dt data-md><dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserverInit" data-dfn-type="dict-member" data-export id="dom-intersectionobserverinit-delay"><code>delay</code></dfn>, <span> of type <a data-link-type="idl-name" href="https://webidl.spec.whatwg.org/#idl-long" id="ref-for-idl-long③">long</a>, defaulting to <code>0</code></span>
+     <dd data-md>
+      <p>A number specifying the minimum delay in milliseconds
+between notifications from the observer for a given target.</p>
+     <dt data-md><dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserverInit" data-dfn-type="dict-member" data-export id="dom-intersectionobserverinit-trackvisibility"><code>trackVisibility</code></dfn>, <span> of type <a data-link-type="idl-name" href="https://webidl.spec.whatwg.org/#idl-boolean" id="ref-for-idl-boolean⑨">boolean</a>, defaulting to <code>false</code></span>
+     <dd data-md>
+      <p>A boolean indicating whether the observer should track <a data-link-type="dfn" href="#visibility" id="ref-for-visibility②">visibility</a>.
+Note that tracking <a data-link-type="dfn" href="#visibility" id="ref-for-visibility③">visibility</a> is likely to be a more expensive operation
+than tracking intersections. It is recommended that this option be used
+only when necessary.</p>
     </dl>
    </div>
    <h2 class="heading settled dfn-paneled" data-dfn-type="dfn" data-level="3" data-lt="Processing Model" data-noexport id="intersection-observer-processing-model"><span class="secno">3. </span><span class="content"> Processing Model</span><a class="self-link" href="#intersection-observer-processing-model" id="ref-for-intersection-observer-processing-model①"></a></h2>
@@ -1365,22 +1446,58 @@ <h4 class="heading settled" data-level="3.1.2" id="element-private-slots"><span
    <p><code class="idl"><a data-link-type="idl" href="https://dom.spec.whatwg.org/#element" id="ref-for-element①④">Element</a></code> objects have an internal <dfn class="dfn-paneled idl-code" data-dfn-for="Element" data-dfn-type="attribute" data-export id="dom-element-registeredintersectionobservers-slot"><code>[[RegisteredIntersectionObservers]]</code></dfn> slot,
 which is initialized to an empty list.
 This list holds <dfn class="dfn-paneled idl-code" data-dfn-type="interface" data-export id="intersectionobserverregistration"><code>IntersectionObserverRegistration</code></dfn> records,
-which have an <dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserverRegistration" data-dfn-type="attribute" data-export id="dom-intersectionobserverregistration-observer"><code>observer</code></dfn> property
-holding an <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver②⓪">IntersectionObserver</a></code>, a <dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserverRegistration" data-dfn-type="attribute" data-export id="dom-intersectionobserverregistration-previousthresholdindex"><code>previousThresholdIndex</code></dfn> property
-holding a number between -1 and the length of the observer’s <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-thresholds" id="ref-for-dom-intersectionobserver-thresholds①">thresholds</a></code> property (inclusive), and
-a <dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserverRegistration" data-dfn-type="attribute" data-export id="dom-intersectionobserverregistration-previousisintersecting"><code>previousIsIntersecting</code></dfn> property holding a boolean.</p>
+which have:</p>
+   <ul>
+    <li data-md>
+     <p>an <dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserverRegistration" data-dfn-type="attribute" data-export id="dom-intersectionobserverregistration-observer"><code>observer</code></dfn> property
+holding an <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver②①">IntersectionObserver</a></code>.</p>
+    <li data-md>
+     <p>a <dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserverRegistration" data-dfn-type="attribute" data-export id="dom-intersectionobserverregistration-previousthresholdindex"><code>previousThresholdIndex</code></dfn> property
+holding a number between -1 and the length of the observer’s <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-thresholds" id="ref-for-dom-intersectionobserver-thresholds①">thresholds</a></code> property (inclusive).</p>
+    <li data-md>
+     <p>a <dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserverRegistration" data-dfn-type="attribute" data-export id="dom-intersectionobserverregistration-previousisintersecting"><code>previousIsIntersecting</code></dfn> property
+holding a boolean.</p>
+    <li data-md>
+     <p>a <dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserverRegistration" data-dfn-type="attribute" data-export id="dom-intersectionobserverregistration-lastupdatetime"><code>lastUpdateTime</code></dfn> property
+holding a <code class="idl"><a data-link-type="idl" href="http://www.w3.org/TR/hr-time/#domhighrestimestamp" id="ref-for-domhighrestimestamp④">DOMHighResTimeStamp</a></code> value.</p>
+    <li data-md>
+     <p>a <dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserverRegistration" data-dfn-type="attribute" data-export id="dom-intersectionobserverregistration-previousisvisible"><code>previousIsVisible</code></dfn> property
+holding a boolean.</p>
+   </ul>
    <h4 class="heading settled" data-level="3.1.3" id="intersection-observer-private-slots"><span class="secno">3.1.3. </span><span class="content"> IntersectionObserver</span><a class="self-link" href="#intersection-observer-private-slots"></a></h4>
-   <p><code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver②①">IntersectionObserver</a></code> objects have internal <dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserver" data-dfn-type="attribute" data-export id="dom-intersectionobserver-queuedentries-slot"><code>[[QueuedEntries]]</code></dfn> and <dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserver" data-dfn-type="attribute" data-export id="dom-intersectionobserver-observationtargets-slot"><code>[[ObservationTargets]]</code></dfn> slots,
-which are initialized to empty lists and an internal <dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserver" data-dfn-type="attribute" data-export id="dom-intersectionobserver-callback-slot"><code>[[callback]]</code></dfn> slot
-which is initialized by <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-intersectionobserver" id="ref-for-dom-intersectionobserver-intersectionobserver">IntersectionObserver(callback, options)</a></code>.
-They also have internal <dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserver" data-dfn-type="attribute" data-export id="dom-intersectionobserver-rootmargin-slot"><code>[[rootMargin]]</code></dfn> and <dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserver" data-dfn-type="attribute" data-export id="dom-intersectionobserver-scrollmargin-slot"><code>[[scrollMargin]]</code></dfn> slots
-which are lists of four pixel lengths or percentages.</p>
+   <p><code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver②②">IntersectionObserver</a></code> objects have the following internal slots:</p>
+   <ul>
+    <li data-md>
+     <p>A <dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserver" data-dfn-type="attribute" data-export id="dom-intersectionobserver-queuedentries-slot"><code>[[QueuedEntries]]</code></dfn> slot
+initialized to an empty list.</p>
+    <li data-md>
+     <p>A <dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserver" data-dfn-type="attribute" data-export id="dom-intersectionobserver-observationtargets-slot"><code>[[ObservationTargets]]</code></dfn> slot
+initialized to an empty list.</p>
+    <li data-md>
+     <p>A <dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserver" data-dfn-type="attribute" data-export id="dom-intersectionobserver-callback-slot"><code>[[callback]]</code></dfn> slot
+which is initialized by <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-intersectionobserver" id="ref-for-dom-intersectionobserver-intersectionobserver">IntersectionObserver(callback, options)</a></code>.</p>
+    <li data-md>
+     <p>A <dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserver" data-dfn-type="attribute" data-export id="dom-intersectionobserver-rootmargin-slot"><code>[[rootMargin]]</code></dfn> slot
+which is a list of four pixel lengths or percentages.</p>
+    <li data-md>
+     <p>A <dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserver" data-dfn-type="attribute" data-export id="dom-intersectionobserver-scrollmargin-slot"><code>[[scrollMargin]]</code></dfn> slot
+which is a list of four pixel lengths or percentages.</p>
+    <li data-md>
+     <p>A <dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserver" data-dfn-type="attribute" data-export id="dom-intersectionobserver-thresholds-slot"><code>[[thresholds]]</code></dfn> slot
+which is initialized by <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-intersectionobserver" id="ref-for-dom-intersectionobserver-intersectionobserver①">IntersectionObserver(callback, options)</a></code>.</p>
+    <li data-md>
+     <p>A <dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserver" data-dfn-type="attribute" data-export id="dom-intersectionobserver-delay-slot"><code>[[delay]]</code></dfn> slot
+which is initialized by <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-intersectionobserver" id="ref-for-dom-intersectionobserver-intersectionobserver②">IntersectionObserver(callback, options)</a></code>.</p>
+    <li data-md>
+     <p>A <dfn class="dfn-paneled idl-code" data-dfn-for="IntersectionObserver" data-dfn-type="attribute" data-export id="dom-intersectionobserver-trackvisibility-slot"><code>[[trackVisibility]]</code></dfn> slot
+which is initialized by <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-intersectionobserver" id="ref-for-dom-intersectionobserver-intersectionobserver③">IntersectionObserver(callback, options)</a></code>.</p>
+   </ul>
    <h3 class="heading settled" data-level="3.2" id="algorithms"><span class="secno">3.2. </span><span class="content"> Algorithms</span><a class="self-link" href="#algorithms"></a></h3>
    <h4 class="heading settled" data-level="3.2.1" id="initialize-new-intersection-observer"><span class="secno">3.2.1. </span><span class="content">Initialize a new IntersectionObserver</span><a class="self-link" href="#initialize-new-intersection-observer"></a></h4>
    <p>To <dfn class="dfn-paneled" data-dfn-type="dfn" data-noexport id="initialize-a-new-intersectionobserver">initialize a new IntersectionObserver</dfn>, given an <code class="idl"><a data-link-type="idl" href="#callbackdef-intersectionobservercallback" id="ref-for-callbackdef-intersectionobservercallback①">IntersectionObserverCallback</a></code> <var>callback</var> and an <code class="idl"><a data-link-type="idl" href="#dictdef-intersectionobserverinit" id="ref-for-dictdef-intersectionobserverinit①">IntersectionObserverInit</a></code> dictionary <var>options</var>, run these steps:</p>
    <ol>
     <li data-md>
-     <p>Let <var>this</var> be a new <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver②②">IntersectionObserver</a></code> object</p>
+     <p>Let <var>this</var> be a new <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver②③">IntersectionObserver</a></code> object</p>
     <li data-md>
      <p>Set <var>this</var>’s internal <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-callback-slot" id="ref-for-dom-intersectionobserver-callback-slot">[[callback]]</a></code> slot to <var>callback</var>.</p>
     <li data-md>
@@ -1405,11 +1522,20 @@ <h4 class="heading settled" data-level="3.2.1" id="initialize-new-intersection-o
     <li data-md>
      <p>The <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-thresholds" id="ref-for-dom-intersectionobserver-thresholds②">thresholds</a></code> attribute getter will return
 this sorted <var>thresholds</var> list.</p>
+    <li data-md>
+     <p>Let <var>delay</var> be the value of <var>options</var>.<code class="idl"><a data-link-type="idl" href="#dom-intersectionobserverinit-delay" id="ref-for-dom-intersectionobserverinit-delay①">delay</a></code>.</p>
+    <li data-md>
+     <p>If <var>options</var>.<code class="idl"><a data-link-type="idl" href="#dom-intersectionobserverinit-trackvisibility" id="ref-for-dom-intersectionobserverinit-trackvisibility①">trackVisibility</a></code> is true
+and <var>delay</var> is less than <code>100</code>, set <var>delay</var> to <code>100</code>.</p>
+    <li data-md>
+     <p>Set <var>this</var>’s internal <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-delay-slot" id="ref-for-dom-intersectionobserver-delay-slot">[[delay]]</a></code> slot to <var>options</var>.<code class="idl"><a data-link-type="idl" href="#dom-intersectionobserverinit-delay" id="ref-for-dom-intersectionobserverinit-delay②">delay</a></code> to <var>delay</var>.</p>
+    <li data-md>
+     <p>Set <var>this</var>’s internal <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-trackvisibility-slot" id="ref-for-dom-intersectionobserver-trackvisibility-slot">[[trackVisibility]]</a></code> slot to <var>options</var>.<code class="idl"><a data-link-type="idl" href="#dom-intersectionobserverinit-trackvisibility" id="ref-for-dom-intersectionobserverinit-trackvisibility②">trackVisibility</a></code>.</p>
     <li data-md>
      <p>Return <var>this</var>.</p>
    </ol>
    <h4 class="heading settled" data-level="3.2.2" id="observe-target-element"><span class="secno">3.2.2. </span><span class="content">Observe a target Element</span><a class="self-link" href="#observe-target-element"></a></h4>
-   <p>To <dfn class="dfn-paneled" data-dfn-type="dfn" data-noexport id="observe-a-target-element">observe a target Element</dfn>, given an <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver②③">IntersectionObserver</a></code> <var>observer</var> and an <code class="idl"><a data-link-type="idl" href="https://dom.spec.whatwg.org/#element" id="ref-for-element①⑤">Element</a></code> <var>target</var>, follow these steps:</p>
+   <p>To <dfn class="dfn-paneled" data-dfn-type="dfn" data-noexport id="observe-a-target-element">observe a target Element</dfn>, given an <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver②④">IntersectionObserver</a></code> <var>observer</var> and an <code class="idl"><a data-link-type="idl" href="https://dom.spec.whatwg.org/#element" id="ref-for-element①⑤">Element</a></code> <var>target</var>, follow these steps:</p>
    <ol>
     <li data-md>
      <p>If <var>target</var> is in <var>observer</var>’s internal <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-observationtargets-slot" id="ref-for-dom-intersectionobserver-observationtargets-slot②">[[ObservationTargets]]</a></code> slot,
@@ -1419,14 +1545,15 @@ <h4 class="heading settled" data-level="3.2.2" id="observe-target-element"><span
 an <code class="idl"><a data-link-type="idl" href="#intersectionobserverregistration" id="ref-for-intersectionobserverregistration①">IntersectionObserverRegistration</a></code> record
 with an <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserverregistration-observer" id="ref-for-dom-intersectionobserverregistration-observer①">observer</a></code> property set to <var>observer</var>,
 a <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserverregistration-previousthresholdindex" id="ref-for-dom-intersectionobserverregistration-previousthresholdindex">previousThresholdIndex</a></code> property set to <code>-1</code>,
-and a <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserverregistration-previousisintersecting" id="ref-for-dom-intersectionobserverregistration-previousisintersecting">previousIsIntersecting</a></code> property set to <code>false</code>.</p>
+a <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserverregistration-previousisintersecting" id="ref-for-dom-intersectionobserverregistration-previousisintersecting">previousIsIntersecting</a></code> property set to false,
+and a <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserverregistration-previousisvisible" id="ref-for-dom-intersectionobserverregistration-previousisvisible">previousIsVisible</a></code> property set to false.</p>
     <li data-md>
      <p>Append <var>intersectionObserverRegistration</var> to <var>target</var>’s internal <code class="idl"><a data-link-type="idl" href="#dom-element-registeredintersectionobservers-slot" id="ref-for-dom-element-registeredintersectionobservers-slot①">[[RegisteredIntersectionObservers]]</a></code> slot.</p>
     <li data-md>
      <p>Add <var>target</var> to <var>observer</var>’s internal <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-observationtargets-slot" id="ref-for-dom-intersectionobserver-observationtargets-slot③">[[ObservationTargets]]</a></code> slot.</p>
    </ol>
    <h4 class="heading settled" data-level="3.2.3" id="unobserve-target-element"><span class="secno">3.2.3. </span><span class="content">Unobserve a target Element</span><a class="self-link" href="#unobserve-target-element"></a></h4>
-   <p>To <dfn class="dfn-paneled" data-dfn-type="dfn" data-noexport id="unobserve-a-target-element">unobserve a target Element</dfn>, given an <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver②④">IntersectionObserver</a></code> <var>observer</var> and an <code class="idl"><a data-link-type="idl" href="https://dom.spec.whatwg.org/#element" id="ref-for-element①⑥">Element</a></code> <var>target</var>, follow these steps:</p>
+   <p>To <dfn class="dfn-paneled" data-dfn-type="dfn" data-noexport id="unobserve-a-target-element">unobserve a target Element</dfn>, given an <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver②⑤">IntersectionObserver</a></code> <var>observer</var> and an <code class="idl"><a data-link-type="idl" href="https://dom.spec.whatwg.org/#element" id="ref-for-element①⑥">Element</a></code> <var>target</var>, follow these steps:</p>
    <ol>
     <li data-md>
      <p>Remove the <code class="idl"><a data-link-type="idl" href="#intersectionobserverregistration" id="ref-for-intersectionobserverregistration②">IntersectionObserverRegistration</a></code> record
@@ -1455,10 +1582,10 @@ <h4 class="heading settled" data-level="3.2.5" id="notify-intersection-observers
     <li data-md>
      <p>Set <var>document</var>’s <a data-link-type="dfn" href="#document-intersectionobservertaskqueued" id="ref-for-document-intersectionobservertaskqueued②">IntersectionObserverTaskQueued</a> flag to false.</p>
     <li data-md>
-     <p>Let <var>notify list</var> be a list of all <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver②⑤">IntersectionObserver</a></code>s
+     <p>Let <var>notify list</var> be a list of all <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver②⑥">IntersectionObserver</a></code>s
 whose <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-root" id="ref-for-dom-intersectionobserver-root⑦">root</a></code> is in the DOM tree of <var>document</var>.</p>
     <li data-md>
-     <p>For each <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver②⑥">IntersectionObserver</a></code> object <var>observer</var> in <var>notify list</var>,
+     <p>For each <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver②⑦">IntersectionObserver</a></code> object <var>observer</var> in <var>notify list</var>,
 run these steps:</p>
      <ol>
       <li data-md>
@@ -1477,7 +1604,7 @@ <h4 class="heading settled" data-level="3.2.5" id="notify-intersection-observers
      </ol>
    </ol>
    <h4 class="heading settled" data-level="3.2.6" id="queue-intersection-observer-entry-algo"><span class="secno">3.2.6. </span><span class="content"> Queue an IntersectionObserverEntry</span><a class="self-link" href="#queue-intersection-observer-entry-algo"></a></h4>
-   <p>To <dfn class="dfn-paneled" data-dfn-type="dfn" data-noexport id="queue-an-intersectionobserverentry">queue an IntersectionObserverEntry</dfn> for an <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver②⑦">IntersectionObserver</a></code> <var>observer</var>, given a <code class="idl"><a data-link-type="idl" href="https://html.spec.whatwg.org/multipage/nav-history-apis.html#dom-document-2" id="ref-for-dom-document-2①⓪">document</a></code> <var>document</var>; <code class="idl"><a data-link-type="idl" href="http://www.w3.org/TR/hr-time/#domhighrestimestamp" id="ref-for-domhighrestimestamp④">DOMHighResTimeStamp</a></code> <var>time</var>; <code class="idl"><a data-link-type="idl" href="https://drafts.fxtf.org/geometry-1/#domrect" id="ref-for-domrect">DOMRect</a></code>s <var>rootBounds</var>, <var>boundingClientRect</var>, <var>intersectionRect</var>, and <var>isIntersecting</var> flag;
+   <p>To <dfn class="dfn-paneled" data-dfn-type="dfn" data-noexport id="queue-an-intersectionobserverentry">queue an IntersectionObserverEntry</dfn> for an <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver②⑧">IntersectionObserver</a></code> <var>observer</var>, given a <code class="idl"><a data-link-type="idl" href="https://html.spec.whatwg.org/multipage/nav-history-apis.html#dom-document-2" id="ref-for-dom-document-2①⓪">document</a></code> <var>document</var>; <code class="idl"><a data-link-type="idl" href="http://www.w3.org/TR/hr-time/#domhighrestimestamp" id="ref-for-domhighrestimestamp⑤">DOMHighResTimeStamp</a></code> <var>time</var>; <code class="idl"><a data-link-type="idl" href="https://drafts.fxtf.org/geometry-1/#domrect" id="ref-for-domrect">DOMRect</a></code>s <var>rootBounds</var>, <var>boundingClientRect</var>, <var>intersectionRect</var>, and <var>isIntersecting</var> flag;
 and an <code class="idl"><a data-link-type="idl" href="https://dom.spec.whatwg.org/#element" id="ref-for-element①⑦">Element</a></code> <var>target</var>;
 run these steps:</p>
    <ol>
@@ -1506,7 +1633,7 @@ <h4 class="heading settled" data-level="3.2.7" id="calculate-intersection-rect-a
       <li data-md>
        <p>Map <var>intersectionRect</var> to the coordinate space of <var>container</var>.</p>
       <li data-md>
-       <p>If <var>container</var> is a <a data-link-type="dfn" href="https://drafts.csswg.org/css-overflow-3/#scroll-container" id="ref-for-scroll-container">scroll container</a>, apply the <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver②⑧">IntersectionObserver</a></code>’s <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-scrollmargin-slot" id="ref-for-dom-intersectionobserver-scrollmargin-slot③">[[scrollMargin]]</a></code> to the <var>container</var>’s clip rect as described in <a data-link-type="dfn" href="#apply-scroll-margin-to-a-scrollport" id="ref-for-apply-scroll-margin-to-a-scrollport">apply scroll margin to a scrollport</a>.</p>
+       <p>If <var>container</var> is a <a data-link-type="dfn" href="https://drafts.csswg.org/css-overflow-3/#scroll-container" id="ref-for-scroll-container">scroll container</a>, apply the <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver②⑨">IntersectionObserver</a></code>’s <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-scrollmargin-slot" id="ref-for-dom-intersectionobserver-scrollmargin-slot③">[[scrollMargin]]</a></code> to the <var>container</var>’s clip rect as described in <a data-link-type="dfn" href="#apply-scroll-margin-to-a-scrollport" id="ref-for-apply-scroll-margin-to-a-scrollport">apply scroll margin to a scrollport</a>.</p>
       <li data-md>
        <p>If <var>container</var> has a <a data-link-type="dfn" href="#intersectionobserver-content-clip" id="ref-for-intersectionobserver-content-clip①">content clip</a> or a css <a data-link-type="dfn" href="http://www.w3.org/TR/css-masking-1/#propdef-clip-path" id="ref-for-propdef-clip-path">clip-path</a> property,
 update <var>intersectionRect</var> by applying <var>container</var>’s clip.</p>
@@ -1524,11 +1651,51 @@ <h4 class="heading settled" data-level="3.2.7" id="calculate-intersection-rect-a
     <li data-md>
      <p>Return <var>intersectionRect</var>.</p>
    </ol>
-   <h4 class="heading settled" data-level="3.2.8" id="update-intersection-observations-algo"><span class="secno">3.2.8. </span><span class="content"> Run the Update Intersection Observations Steps</span><a class="self-link" href="#update-intersection-observations-algo"></a></h4>
-   <p>To <dfn data-dfn-type="dfn" data-export id="run-the-update-intersection-observations-steps">run the update intersection observations steps<a class="self-link" href="#run-the-update-intersection-observations-steps"></a></dfn> for a <a data-link-type="dfn" href="https://html.spec.whatwg.org/multipage/dom.html#document" id="ref-for-document③">Document</a> <var>document</var> given a timestamp <var>time</var>, run these steps:</p>
+   <h4 class="heading settled" data-level="3.2.8" id="calculate-visibility-algo"><span class="secno">3.2.8. </span><span class="content"> Compute whether a Target is unoccluded, untransformed, unfiltered, and opaque.</span><a class="self-link" href="#calculate-visibility-algo"></a></h4>
+   <p>To compute the <dfn class="dfn-paneled" data-dfn-type="dfn" data-noexport id="visibility">visibility</dfn> of a <a data-link-type="dfn" href="#intersectionobserver-target" id="ref-for-intersectionobserver-target①③">target</a>, run these steps:</p>
+   <ol>
+    <li data-md>
+     <p>If the <var>observer</var>’s <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-trackvisibility" id="ref-for-dom-intersectionobserver-trackvisibility①">trackVisibility</a></code> attribute is false, return false.</p>
+    <li data-md>
+     <p>If the <a data-link-type="dfn" href="#intersectionobserver-target" id="ref-for-intersectionobserver-target①④">target</a> has an <a data-link-type="dfn" href="#effective-transformation-matrix" id="ref-for-effective-transformation-matrix">effective transformation matrix</a> other than a 2D translation or proportional 2D upscaling, return false.</p>
+    <li data-md>
+     <p>If the <a data-link-type="dfn" href="#intersectionobserver-target" id="ref-for-intersectionobserver-target①⑤">target</a>, or any element in its <a data-link-type="dfn" href="https://drafts.csswg.org/css-display/#containing-block-chain" id="ref-for-containing-block-chain①">containing block chain</a>, has an effective opacity other than 100%, return false.</p>
+    <li data-md>
+     <p>If the <a data-link-type="dfn" href="#intersectionobserver-target" id="ref-for-intersectionobserver-target①⑥">target</a>, or any element in its <a data-link-type="dfn" href="https://drafts.csswg.org/css-display/#containing-block-chain" id="ref-for-containing-block-chain②">containing block chain</a>, has any filters applied, return false.</p>
+    <li data-md>
+     <p>If the implementation cannot guarantee that the <a data-link-type="dfn" href="#intersectionobserver-target" id="ref-for-intersectionobserver-target①⑦">target</a> is completely unoccluded by other page content, return false.</p>
+   </ol>
+   <p class="note" role="note"><span class="marker">Note:</span> Implementations should use the <a data-link-type="dfn" href="https://drafts.csswg.org/css-overflow-3/#ink-overflow-rectangle" id="ref-for-ink-overflow-rectangle">ink overflow rectangle</a> of page content when determining whether a <a data-link-type="dfn" href="#intersectionobserver-target" id="ref-for-intersectionobserver-target①⑧">target</a> is occluded. For blur effects, which have theoretically infinite extent, the <a data-link-type="dfn" href="https://drafts.csswg.org/css-overflow-3/#ink-overflow-rectangle" id="ref-for-ink-overflow-rectangle①">ink overflow rectangle</a> is defined by the finite-area approximation described for the <a data-link-type="dfn" href="https://drafts.fxtf.org/filter-effects/#funcdef-filter-blur" id="ref-for-funcdef-filter-blur">blur</a> filter function.</p>
+   <ol start="6">
+    <li data-md>
+     <p>Return true.</p>
+   </ol>
+   <h4 class="heading settled" data-level="3.2.9" id="calculate-effective-transformation-matrix"><span class="secno">3.2.9. </span><span class="content">Calculate a <a data-link-type="dfn" href="#intersectionobserver-target" id="ref-for-intersectionobserver-target①⑨">target</a>’s Effective Transformation Matrix</span><a class="self-link" href="#calculate-effective-transformation-matrix"></a></h4>
+    To compute the <dfn class="dfn-paneled" data-dfn-type="dfn" data-noexport id="effective-transformation-matrix">effective transformation matrix</dfn> of a <a data-link-type="dfn" href="#intersectionobserver-target" id="ref-for-intersectionobserver-target②⓪">target</a>, run these steps: 
    <ol>
     <li data-md>
-     <p>Let <var>observer list</var> be a list of all <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver②⑨">IntersectionObserver</a></code>s
+     <p>Let <var>matrix</var> be the <a data-link-type="dfn" href="https://drafts.csswg.org/css-transforms-1/#serialization-of-the-computed-value" id="ref-for-serialization-of-the-computed-value">serialization</a> of the <a data-link-type="dfn" href="https://drafts.csswg.org/css-transforms-1/#identity-transform-function" id="ref-for-identity-transform-function">identity transform function</a>.</p>
+    <li data-md>
+     <p>Let <var>container</var> be the target.</p>
+    <li data-md>
+     <p>While <var>container</var> is not the <a data-link-type="dfn" href="#intersectionobserver-intersection-root" id="ref-for-intersectionobserver-intersection-root①⑤">intersection root</a>:</p>
+     <ol>
+      <li data-md>
+       <p>Set <var>t</var> to <var>container</var>’s <a data-link-type="dfn" href="https://drafts.csswg.org/css-transforms-1/#transformation-matrix" id="ref-for-transformation-matrix">transformation matrix</a>.</p>
+      <li data-md>
+       <p>Set <var>matrix</var> to <var>t</var> <a data-link-type="dfn" href="https://drafts.csswg.org/css-transforms-1/#post-multiplied" id="ref-for-post-multiplied">post-multiplied</a> by <var>matrix</var>.</p>
+      <li data-md>
+       <p>If <var>container</var> is the root element of a <a data-link-type="dfn" href="https://html.spec.whatwg.org/multipage/browsers.html#nested-browsing-context" id="ref-for-nested-browsing-context②">nested browsing context</a>,
+       update <var>container</var> to be the <a data-link-type="dfn" href="https://html.spec.whatwg.org/multipage/browsers.html#browsing-context-container" id="ref-for-browsing-context-container①">browsing context container</a> of <var>container</var>. Otherwise, update <var>container</var> to be the <a data-link-type="dfn" href="https://drafts.csswg.org/css-box/#containing-block" id="ref-for-containing-block②">containing block</a> of <var>container</var>.</p>
+     </ol>
+    <li data-md>
+     <p>Return <var>matrix</var>.</p>
+   </ol>
+   <h4 class="heading settled" data-level="3.2.10" id="update-intersection-observations-algo"><span class="secno">3.2.10. </span><span class="content"> Run the Update Intersection Observations Steps</span><a class="self-link" href="#update-intersection-observations-algo"></a></h4>
+   <p>To <dfn class="dfn-paneled" data-dfn-type="dfn" data-export id="run-the-update-intersection-observations-steps">run the update intersection observations steps</dfn> for a <a data-link-type="dfn" href="https://html.spec.whatwg.org/multipage/dom.html#document" id="ref-for-document③">Document</a> <var>document</var> given a timestamp <var>time</var>, run these steps:</p>
+   <ol>
+    <li data-md>
+     <p>Let <var>observer list</var> be a list of all <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver③⓪">IntersectionObserver</a></code>s
 whose <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-root" id="ref-for-dom-intersectionobserver-root⑧">root</a></code> is in the DOM tree of <var>document</var>.
 For the <a data-link-type="dfn" href="https://html.spec.whatwg.org/multipage/browsers.html#top-level-browsing-context" id="ref-for-top-level-browsing-context④">top-level browsing context</a>, this includes <a data-link-type="dfn" href="#intersectionobserver-implicit-root-observer" id="ref-for-intersectionobserver-implicit-root-observer③">implicit root observers</a>.</p>
     <li data-md>
@@ -1539,6 +1706,14 @@ <h4 class="heading settled" data-level="3.2.8" id="update-intersection-observati
       <li data-md>
        <p>For each <var>target</var> in <var>observer</var>’s internal <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-observationtargets-slot" id="ref-for-dom-intersectionobserver-observationtargets-slot⑤">[[ObservationTargets]]</a></code> slot, processed in the same order that <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-observe" id="ref-for-dom-intersectionobserver-observe③">observe()</a></code> was called on each <var>target</var>:</p>
        <ol>
+        <li data-md>
+         <p>Let <var>registration</var> be the <code class="idl"><a data-link-type="idl" href="#intersectionobserverregistration" id="ref-for-intersectionobserverregistration③">IntersectionObserverRegistration</a></code> record
+	in <var>target</var>’s internal <code class="idl"><a data-link-type="idl" href="#dom-element-registeredintersectionobservers-slot" id="ref-for-dom-element-registeredintersectionobservers-slot③">[[RegisteredIntersectionObservers]]</a></code> slot
+	whose <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserverregistration-observer" id="ref-for-dom-intersectionobserverregistration-observer③">observer</a></code> property is equal to <var>observer</var>.</p>
+        <li data-md>
+         <p>If <code>(<var>time</var> - <var>registration</var>.<code class="idl"><a data-link-type="idl" href="#dom-intersectionobserverregistration-lastupdatetime" id="ref-for-dom-intersectionobserverregistration-lastupdatetime">lastUpdateTime</a></code> &lt; <var>observer</var>.<code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-delay" id="ref-for-dom-intersectionobserver-delay①">delay</a></code>)</code>, skip further processing for <var>target</var>.</p>
+        <li data-md>
+         <p>Set <var>registration</var>.<code class="idl"><a data-link-type="idl" href="#dom-intersectionobserverregistration-lastupdatetime" id="ref-for-dom-intersectionobserverregistration-lastupdatetime①">lastUpdateTime</a></code> to <var>time</var>.</p>
         <li data-md>
          <p>Let:</p>
          <ul>
@@ -1552,16 +1727,16 @@ <h4 class="heading settled" data-level="3.2.8" id="update-intersection-observati
            <p><var>intersectionRect</var> be a <code class="idl"><a data-link-type="idl" href="https://drafts.fxtf.org/geometry-1/#domrectreadonly" id="ref-for-domrectreadonly⑧">DOMRectReadOnly</a></code> with <var>x</var>, <var>y</var>, <var>width</var>, and <var>height</var> set to 0.</p>
          </ul>
         <li data-md>
-         <p>If the <a data-link-type="dfn" href="#intersectionobserver-intersection-root" id="ref-for-intersectionobserver-intersection-root①⑤">intersection root</a> is not the <a data-link-type="dfn" href="#intersectionobserver-implicit-root" id="ref-for-intersectionobserver-implicit-root①">implicit root</a>,
-and <var>target</var> is not in the same <code class="idl"><a data-link-type="idl" href="https://html.spec.whatwg.org/multipage/nav-history-apis.html#dom-document-2" id="ref-for-dom-document-2①⑤">document</a></code> as the <a data-link-type="dfn" href="#intersectionobserver-intersection-root" id="ref-for-intersectionobserver-intersection-root①⑥">intersection root</a>,
+         <p>If the <a data-link-type="dfn" href="#intersectionobserver-intersection-root" id="ref-for-intersectionobserver-intersection-root①⑥">intersection root</a> is not the <a data-link-type="dfn" href="#intersectionobserver-implicit-root" id="ref-for-intersectionobserver-implicit-root①">implicit root</a>,
+and <var>target</var> is not in the same <code class="idl"><a data-link-type="idl" href="https://html.spec.whatwg.org/multipage/nav-history-apis.html#dom-document-2" id="ref-for-dom-document-2①⑤">document</a></code> as the <a data-link-type="dfn" href="#intersectionobserver-intersection-root" id="ref-for-intersectionobserver-intersection-root①⑦">intersection root</a>,
 skip to step 11.</p>
         <li data-md>
-         <p>If the <a data-link-type="dfn" href="#intersectionobserver-intersection-root" id="ref-for-intersectionobserver-intersection-root①⑦">intersection root</a> is an <code class="idl"><a data-link-type="idl" href="https://dom.spec.whatwg.org/#element" id="ref-for-element①⑧">Element</a></code>,
-and <var>target</var> is not a descendant of the <a data-link-type="dfn" href="#intersectionobserver-intersection-root" id="ref-for-intersectionobserver-intersection-root①⑧">intersection root</a> in the <a data-link-type="dfn" href="https://drafts.csswg.org/css-display/#containing-block-chain" id="ref-for-containing-block-chain①">containing block chain</a>, skip to step 11.</p>
+         <p>If the <a data-link-type="dfn" href="#intersectionobserver-intersection-root" id="ref-for-intersectionobserver-intersection-root①⑧">intersection root</a> is an <code class="idl"><a data-link-type="idl" href="https://dom.spec.whatwg.org/#element" id="ref-for-element①⑧">Element</a></code>,
+and <var>target</var> is not a descendant of the <a data-link-type="dfn" href="#intersectionobserver-intersection-root" id="ref-for-intersectionobserver-intersection-root①⑨">intersection root</a> in the <a data-link-type="dfn" href="https://drafts.csswg.org/css-display/#containing-block-chain" id="ref-for-containing-block-chain③">containing block chain</a>, skip to step 11.</p>
         <li data-md>
          <p>Set <var>targetRect</var> to the <code class="idl"><a data-link-type="idl" href="https://drafts.fxtf.org/geometry-1/#domrectreadonly" id="ref-for-domrectreadonly⑨">DOMRectReadOnly</a></code> obtained by <a data-link-type="dfn" href="https://drafts.csswg.org/cssom-view-1/#element-get-the-bounding-box" id="ref-for-element-get-the-bounding-box④">getting the bounding box</a> for <var>target</var>.</p>
         <li data-md>
-         <p>Let <var>intersectionRect</var> be the result of running the <a data-link-type="dfn" href="#compute-the-intersection" id="ref-for-compute-the-intersection">compute the intersection</a> algorithm on <var>target</var> and <var>observer</var>’s <a data-link-type="dfn" href="#intersectionobserver-intersection-root" id="ref-for-intersectionobserver-intersection-root①⑨">intersection root</a>.</p>
+         <p>Let <var>intersectionRect</var> be the result of running the <a data-link-type="dfn" href="#compute-the-intersection" id="ref-for-compute-the-intersection">compute the intersection</a> algorithm on <var>target</var> and <var>observer</var>’s <a data-link-type="dfn" href="#intersectionobserver-intersection-root" id="ref-for-intersectionobserver-intersection-root②⓪">intersection root</a>.</p>
         <li data-md>
          <p>Let <var>targetArea</var> be <var>targetRect</var>’s area.</p>
         <li data-md>
@@ -1575,39 +1750,43 @@ <h4 class="heading settled" data-level="3.2.8" id="update-intersection-observati
         <li data-md>
          <p>Set <var>thresholdIndex</var> to the index of the first entry in <var>observer</var>.<code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-thresholds" id="ref-for-dom-intersectionobserver-thresholds③">thresholds</a></code> whose value is greater than <var>intersectionRatio</var>, or the length of <var>observer</var>.<code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-thresholds" id="ref-for-dom-intersectionobserver-thresholds④">thresholds</a></code> if <var>intersectionRatio</var> is greater than or equal to the last entry in <var>observer</var>.<code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-thresholds" id="ref-for-dom-intersectionobserver-thresholds⑤">thresholds</a></code>.</p>
         <li data-md>
-         <p>Let <var>intersectionObserverRegistration</var> be the <code class="idl"><a data-link-type="idl" href="#intersectionobserverregistration" id="ref-for-intersectionobserverregistration③">IntersectionObserverRegistration</a></code> record
-in <var>target</var>’s internal <code class="idl"><a data-link-type="idl" href="#dom-element-registeredintersectionobservers-slot" id="ref-for-dom-element-registeredintersectionobservers-slot③">[[RegisteredIntersectionObservers]]</a></code> slot
-whose <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserverregistration-observer" id="ref-for-dom-intersectionobserverregistration-observer③">observer</a></code> property is equal to <var>observer</var>.</p>
+         <p>Let <var>isVisible</var> be the result of running the <a data-link-type="dfn" href="#visibility" id="ref-for-visibility④">visibility</a> algorithm on <var>target</var>.</p>
+        <li data-md>
+         <p>Let <var>previousThresholdIndex</var> be the <var>registration</var>’s <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserverregistration-previousthresholdindex" id="ref-for-dom-intersectionobserverregistration-previousthresholdindex①">previousThresholdIndex</a></code> property.</p>
+        <li data-md>
+         <p>Let <var>previousIsIntersecting</var> be the <var>registration</var>’s <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserverregistration-previousisintersecting" id="ref-for-dom-intersectionobserverregistration-previousisintersecting①">previousIsIntersecting</a></code> property.</p>
         <li data-md>
-         <p>Let <var>previousThresholdIndex</var> be the <var>intersectionObserverRegistration</var>’s <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserverregistration-previousthresholdindex" id="ref-for-dom-intersectionobserverregistration-previousthresholdindex①">previousThresholdIndex</a></code> property.</p>
+         <p>Let <var>previousIsVisible</var> be the <var>registration</var>’s <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserverregistration-previousisvisible" id="ref-for-dom-intersectionobserverregistration-previousisvisible①">previousIsVisible</a></code> property.</p>
         <li data-md>
-         <p>Let <var>previousIsIntersecting</var> be the <var>intersectionObserverRegistration</var>’s <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserverregistration-previousisintersecting" id="ref-for-dom-intersectionobserverregistration-previousisintersecting①">previousIsIntersecting</a></code> property.</p>
+         <p>If <var>thresholdIndex</var> does not equal <var>previousThresholdIndex</var>,
+or if <var>isIntersecting</var> does not equal <var>previousIsIntersecting</var>,
+or if <var>isVisible</var> does not equal <var>previousIsVisible</var>, <a data-link-type="dfn" href="#queue-an-intersectionobserverentry" id="ref-for-queue-an-intersectionobserverentry">queue an IntersectionObserverEntry</a>,
+passing in <var>observer</var>, <var>time</var>, <var>rootBounds</var>, <var>targetRect</var>, <var>intersectionRect</var>, <var>isIntersecting</var>, <var>isVisible</var>, and <var>target</var>.</p>
         <li data-md>
-         <p>If <var>thresholdIndex</var> does not equal <var>previousThresholdIndex</var> or if <var>isIntersecting</var> does not equal <var>previousIsIntersecting</var>, <a data-link-type="dfn" href="#queue-an-intersectionobserverentry" id="ref-for-queue-an-intersectionobserverentry">queue an IntersectionObserverEntry</a>,
-passing in <var>observer</var>, <var>time</var>, <var>rootBounds</var>, <var>targetRect</var>, <var>intersectionRect</var>, <var>isIntersecting</var>, and <var>target</var>.</p>
+         <p>Assign <var>thresholdIndex</var> to <var>registration</var>’s <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserverregistration-previousthresholdindex" id="ref-for-dom-intersectionobserverregistration-previousthresholdindex②">previousThresholdIndex</a></code> property.</p>
         <li data-md>
-         <p>Assign <var>thresholdIndex</var> to <var>intersectionObserverRegistration</var>’s <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserverregistration-previousthresholdindex" id="ref-for-dom-intersectionobserverregistration-previousthresholdindex②">previousThresholdIndex</a></code> property.</p>
+         <p>Assign <var>isIntersecting</var> to <var>registration</var>’s <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserverregistration-previousisintersecting" id="ref-for-dom-intersectionobserverregistration-previousisintersecting②">previousIsIntersecting</a></code> property.</p>
         <li data-md>
-         <p>Assign <var>isIntersecting</var> to <var>intersectionObserverRegistration</var>’s <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserverregistration-previousisintersecting" id="ref-for-dom-intersectionobserverregistration-previousisintersecting②">previousIsIntersecting</a></code> property.</p>
+         <p>Assign <var>isVisible</var> to <var>registration</var>’s <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserverregistration-previousisvisible" id="ref-for-dom-intersectionobserverregistration-previousisvisible②">previousIsVisible</a></code> property.</p>
        </ol>
      </ol>
    </ol>
    <h3 class="heading settled" data-level="3.3" id="lifetime"><span class="secno">3.3. </span><span class="content"> IntersectionObserver Lifetime</span><a class="self-link" href="#lifetime"></a></h3>
-   <p>An <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver③⓪">IntersectionObserver</a></code> will remain alive until both of these conditions hold:</p>
+   <p>An <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver③①">IntersectionObserver</a></code> will remain alive until both of these conditions hold:</p>
    <ul>
     <li>There are no scripting references to the observer.
     <li>The observer is not observing any targets. 
    </ul>
-   <p>An <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver③①">IntersectionObserver</a></code> will continue observing a target until either the observer’s <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-unobserve" id="ref-for-dom-intersectionobserver-unobserve③">unobserve()</a></code> method is called with the target as argument; or the observer’s <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-disconnect" id="ref-for-dom-intersectionobserver-disconnect②">disconnect()</a></code> is called.</p>
+   <p>An <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver③②">IntersectionObserver</a></code> will continue observing a target until either the observer’s <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-unobserve" id="ref-for-dom-intersectionobserver-unobserve③">unobserve()</a></code> method is called with the target as argument; or the observer’s <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-disconnect" id="ref-for-dom-intersectionobserver-disconnect②">disconnect()</a></code> is called.</p>
    <h3 class="heading settled" data-level="3.4" id="external-spec-integrations"><span class="secno">3.4. </span><span class="content"> External Spec Integrations</span><a class="self-link" href="#external-spec-integrations"></a></h3>
    <h4 class="heading settled" data-level="3.4.1" id="event-loop"><span class="secno">3.4.1. </span><span class="content"> HTML Processing Model: Event Loop</span><a class="self-link" href="#event-loop"></a></h4>
    <p>An Intersection Observer processing step exists as a substep
 within the "<i>Update the rendering</i>" step,
 in the <a data-link-type="dfn" href="https://html.spec.whatwg.org/multipage/webappapis.html#event-loop-processing-model" id="ref-for-event-loop-processing-model">HTML Event Loops Processing Model</a>.</p>
    <h4 class="heading settled" data-level="3.4.2" id="pending-initial-observation"><span class="secno">3.4.2. </span><span class="content">Pending initial IntersectionObserver targets</span><a class="self-link" href="#pending-initial-observation"></a></h4>
-    A <code class="idl"><a data-link-type="idl" href="https://html.spec.whatwg.org/multipage/nav-history-apis.html#dom-document-2" id="ref-for-dom-document-2①⑥">document</a></code> is said to have <dfn class="dfn-paneled" data-dfn-type="dfn" data-noexport id="pending-initial-intersectionobserver-targets">pending initial IntersectionObserver targets</dfn> if there is at least one <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver③②">IntersectionObserver</a></code> meeting these criteria: 
+    A <code class="idl"><a data-link-type="idl" href="https://html.spec.whatwg.org/multipage/nav-history-apis.html#dom-document-2" id="ref-for-dom-document-2①⑥">document</a></code> is said to have <dfn class="dfn-paneled" data-dfn-type="dfn" data-noexport id="pending-initial-intersectionobserver-targets">pending initial IntersectionObserver targets</dfn> if there is at least one <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver③③">IntersectionObserver</a></code> meeting these criteria: 
    <ol>
-    <li>The <var>observer</var>’s <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver③③">root</a></code> is in the <var>document</var> (for the <a data-link-type="dfn" href="https://html.spec.whatwg.org/multipage/browsers.html#top-level-browsing-context" id="ref-for-top-level-browsing-context⑤">top-level browsing context</a>, this includes <a data-link-type="dfn" href="#intersectionobserver-implicit-root-observer" id="ref-for-intersectionobserver-implicit-root-observer④">implicit root observers</a>). 
+    <li>The <var>observer</var>’s <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver③④">root</a></code> is in the <var>document</var> (for the <a data-link-type="dfn" href="https://html.spec.whatwg.org/multipage/browsers.html#top-level-browsing-context" id="ref-for-top-level-browsing-context⑤">top-level browsing context</a>, this includes <a data-link-type="dfn" href="#intersectionobserver-implicit-root-observer" id="ref-for-intersectionobserver-implicit-root-observer④">implicit root observers</a>). 
     <li>The <var>observer</var> has at least one <var>target</var> in its <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-observationtargets-slot" id="ref-for-dom-intersectionobserver-observationtargets-slot⑥">[[ObservationTargets]]</a></code> slot for which
 		    no <code class="idl"><a data-link-type="idl" href="#intersectionobserverentry" id="ref-for-intersectionobserverentry⑤">IntersectionObserverEntry</a></code> has yet been queued. 
    </ol>
@@ -1635,12 +1814,12 @@ <h2 class="heading settled" data-level="5" id="privacy"><span class="secno">5. <
 which may be used to deduce the user’s hardware configuration.
 The motivation for disabling the effects of <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-rootmargin" id="ref-for-dom-intersectionobserver-rootmargin④">rootMargin</a></code> and <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserver-scrollmargin" id="ref-for-dom-intersectionobserver-scrollmargin③">scrollMargin</a></code>, and suppressing <code class="idl"><a data-link-type="idl" href="#dom-intersectionobserverentry-rootbounds" id="ref-for-dom-intersectionobserverentry-rootbounds①">rootBounds</a></code> for <a data-link-type="dfn" href="#intersectionobserver-cross-origin-domain-target" id="ref-for-intersectionobserver-cross-origin-domain-target③">cross-origin-domain targets</a> is to prevent such probing.</p>
    </ul>
-   <p>It should be noted that prior to <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver③④">IntersectionObserver</a></code>, web developers
+   <p>It should be noted that prior to <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver③⑤">IntersectionObserver</a></code>, web developers
 used other API’s in very ingenious (and grotesque) ways to tease out the information
-available from <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver③⑤">IntersectionObserver</a></code>. As a purely practical matter, this API
+available from <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver③⑥">IntersectionObserver</a></code>. As a purely practical matter, this API
 does not reveal any information that was not already available by other means.</p>
-   <p>Another consideration is that <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver③⑥">IntersectionObserver</a></code> uses <code class="idl"><a data-link-type="idl" href="http://www.w3.org/TR/hr-time/#domhighrestimestamp" id="ref-for-domhighrestimestamp⑤">DOMHighResTimeStamp</a></code>,
-which has privacy and security considerations of its own. It is however unlikely that <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver③⑦">IntersectionObserver</a></code> is vulnerable to timing-related exploits. Timestamps are generated
+   <p>Another consideration is that <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver③⑦">IntersectionObserver</a></code> uses <code class="idl"><a data-link-type="idl" href="http://www.w3.org/TR/hr-time/#domhighrestimestamp" id="ref-for-domhighrestimestamp⑥">DOMHighResTimeStamp</a></code>,
+which has privacy and security considerations of its own. It is however unlikely that <code class="idl"><a data-link-type="idl" href="#intersectionobserver" id="ref-for-intersectionobserver③⑧">IntersectionObserver</a></code> is vulnerable to timing-related exploits. Timestamps are generated
 at most once per rendering update (see <a href="#event-loop">§ 3.4.1 HTML Processing Model: Event Loop</a>), which is far too
 infrequent for the familiar kind of timing attack.</p>
    <h2 class="heading settled" data-level="6" id="internationalization"><span class="secno">6. </span><span class="content">Internationalization</span><a class="self-link" href="#internationalization"></a></h2>
@@ -1693,7 +1872,7 @@ <h3 class="no-ref no-num heading settled" id="w3c-conformant-algorithms"><span c
     Implementers are encouraged to optimize. </p>
    </section>
   </div>
-<script src="https://www.w3.org/scripts/TR/2021/fixup.js"></script>
+  <script src="https://www.w3.org/scripts/TR/2021/fixup.js"></script>
   <h2 class="no-num no-ref heading settled" id="index"><span class="content">Index</span><a class="self-link" href="#index"></a></h2>
   <h3 class="no-num no-ref heading settled" id="index-defined-here"><span class="content">Terms defined by this specification</span><a class="self-link" href="#index-defined-here"></a></h3>
   <ul class="index">
@@ -1711,7 +1890,15 @@ <h3 class="no-num no-ref heading settled" id="index-defined-here"><span class="c
    <li><a href="#dom-intersectionobserverentry-intersectionobserverentry">constructor(intersectionObserverEntryInit)</a><span>, in § 2.3</span>
    <li><a href="#intersectionobserver-content-clip">content clip</a><span>, in § 2.2</span>
    <li><a href="#intersectionobserver-cross-origin-domain-target">cross-origin-domain target</a><span>, in § 2.2</span>
+   <li><a href="#dom-intersectionobserver-delay-slot">[[delay]]</a><span>, in § 3.1.3</span>
+   <li>
+    delay
+    <ul>
+     <li><a href="#dom-intersectionobserver-delay">attribute for IntersectionObserver</a><span>, in § 2.2</span>
+     <li><a href="#dom-intersectionobserverinit-delay">dict-member for IntersectionObserverInit</a><span>, in § 2.4</span>
+    </ul>
    <li><a href="#dom-intersectionobserver-disconnect">disconnect()</a><span>, in § 2.2</span>
+   <li><a href="#effective-transformation-matrix">effective transformation matrix</a><span>, in § 3.2.9</span>
    <li><a href="#intersectionobserver-explicit-root-observer">explicit root observer</a><span>, in § 2.2</span>
    <li><a href="#intersectionobserver-implicit-root">implicit root</a><span>, in § 2.2</span>
    <li><a href="#intersectionobserver-implicit-root-observer">implicit root observer</a><span>, in § 2.2</span>
@@ -1748,6 +1935,13 @@ <h3 class="no-num no-ref heading settled" id="index-defined-here"><span class="c
      <li><a href="#dom-intersectionobserverentry-isintersecting">attribute for IntersectionObserverEntry</a><span>, in § 2.3</span>
      <li><a href="#dom-intersectionobserverentryinit-isintersecting">dict-member for IntersectionObserverEntryInit</a><span>, in § 2.3</span>
     </ul>
+   <li>
+    isVisible
+    <ul>
+     <li><a href="#dom-intersectionobserverentry-isvisible">attribute for IntersectionObserverEntry</a><span>, in § 2.3</span>
+     <li><a href="#dom-intersectionobserverentryinit-isvisible">dict-member for IntersectionObserverEntryInit</a><span>, in § 2.3</span>
+    </ul>
+   <li><a href="#dom-intersectionobserverregistration-lastupdatetime">lastUpdateTime</a><span>, in § 3.1.2</span>
    <li><a href="#notify-intersection-observers">notify intersection observers</a><span>, in § 3.2.5</span>
    <li><a href="#dom-intersectionobserver-observationtargets-slot">[[ObservationTargets]]</a><span>, in § 3.1.3</span>
    <li><a href="#observe-a-target-element">observe a target Element</a><span>, in § 3.2.2</span>
@@ -1756,6 +1950,7 @@ <h3 class="no-num no-ref heading settled" id="index-defined-here"><span class="c
    <li><a href="#parse-a-margin">parse a margin</a><span>, in § 2.2</span>
    <li><a href="#pending-initial-intersectionobserver-targets">pending initial IntersectionObserver targets</a><span>, in § 3.4.2</span>
    <li><a href="#dom-intersectionobserverregistration-previousisintersecting">previousIsIntersecting</a><span>, in § 3.1.2</span>
+   <li><a href="#dom-intersectionobserverregistration-previousisvisible">previousIsVisible</a><span>, in § 3.1.2</span>
    <li><a href="#dom-intersectionobserverregistration-previousthresholdindex">previousThresholdIndex</a><span>, in § 3.1.2</span>
    <li><a href="#intersection-observer-processing-model">Processing Model</a><span>, in § 2.4</span>
    <li><a href="#queue-an-intersectionobserverentry">queue an IntersectionObserverEntry</a><span>, in § 3.2.6</span>
@@ -1782,7 +1977,7 @@ <h3 class="no-num no-ref heading settled" id="index-defined-here"><span class="c
      <li><a href="#dom-intersectionobserver-rootmargin">attribute for IntersectionObserver</a><span>, in § 2.2</span>
      <li><a href="#dom-intersectionobserverinit-rootmargin">dict-member for IntersectionObserverInit</a><span>, in § 2.4</span>
     </ul>
-   <li><a href="#run-the-update-intersection-observations-steps">run the update intersection observations steps</a><span>, in § 3.2.8</span>
+   <li><a href="#run-the-update-intersection-observations-steps">run the update intersection observations steps</a><span>, in § 3.2.10</span>
    <li><a href="#intersectionobserver-same-origin-domain-target">same-origin-domain target</a><span>, in § 2.2</span>
    <li><a href="#dom-intersectionobserver-scrollmargin-slot">[[scrollMargin]]</a><span>, in § 3.1.3</span>
    <li>
@@ -1800,6 +1995,7 @@ <h3 class="no-num no-ref heading settled" id="index-defined-here"><span class="c
      <li><a href="#dom-intersectionobserverentryinit-target">dict-member for IntersectionObserverEntryInit</a><span>, in § 2.3</span>
     </ul>
    <li><a href="#dom-intersectionobserverinit-threshold">threshold</a><span>, in § 2.4</span>
+   <li><a href="#dom-intersectionobserver-thresholds-slot">[[thresholds]]</a><span>, in § 3.1.3</span>
    <li><a href="#dom-intersectionobserver-thresholds">thresholds</a><span>, in § 2.2</span>
    <li>
     time
@@ -1807,8 +2003,16 @@ <h3 class="no-num no-ref heading settled" id="index-defined-here"><span class="c
      <li><a href="#dom-intersectionobserverentry-time">attribute for IntersectionObserverEntry</a><span>, in § 2.3</span>
      <li><a href="#dom-intersectionobserverentryinit-time">dict-member for IntersectionObserverEntryInit</a><span>, in § 2.3</span>
     </ul>
+   <li><a href="#dom-intersectionobserver-trackvisibility-slot">[[trackVisibility]]</a><span>, in § 3.1.3</span>
+   <li>
+    trackVisibility
+    <ul>
+     <li><a href="#dom-intersectionobserver-trackvisibility">attribute for IntersectionObserver</a><span>, in § 2.2</span>
+     <li><a href="#dom-intersectionobserverinit-trackvisibility">dict-member for IntersectionObserverInit</a><span>, in § 2.4</span>
+    </ul>
    <li><a href="#unobserve-a-target-element">unobserve a target Element</a><span>, in § 3.2.3</span>
    <li><a href="#dom-intersectionobserver-unobserve">unobserve(target)</a><span>, in § 2.2</span>
+   <li><a href="#visibility">visibility</a><span>, in § 3.2.8</span>
   </ul>
   <h3 class="no-num no-ref heading settled" id="index-defined-elsewhere"><span class="content">Terms defined by reference</span><a class="self-link" href="#index-defined-elsewhere"></a></h3>
   <ul class="index">
@@ -1818,6 +2022,7 @@ <h3 class="no-num no-ref heading settled" id="index-defined-elsewhere"><span cla
      <li><span class="dfn-paneled" id="3b11702b">DOMHighResTimeStamp</span>
      <li><span class="dfn-paneled" id="097f5617">RangeError</span>
      <li><span class="dfn-paneled" id="90867675">SyntaxError</span>
+     <li><span class="dfn-paneled" id="641304c2">blur</span>
      <li><span class="dfn-paneled" id="faf954d6">browsing context</span>
      <li><span class="dfn-paneled" id="7939ecaf">browsing context container</span>
      <li><span class="dfn-paneled" id="382d14c8">callback this value</span>
@@ -1829,6 +2034,8 @@ <h3 class="no-num no-ref heading settled" id="index-defined-elsewhere"><span cla
      <li><span class="dfn-paneled" id="c6d19e56">event loop</span>
      <li><span class="dfn-paneled" id="a192c757">fully active</span>
      <li><span class="dfn-paneled" id="b3778518">html event loops processing model</span>
+     <li><span class="dfn-paneled" id="fdf79120">identity transform function</span>
+     <li><span class="dfn-paneled" id="3c7a8d55">ink overflow rectangle</span>
      <li><span class="dfn-paneled" id="10e56401">list of the descendant browsing contexts</span>
      <li><span class="dfn-paneled" id="25d33108">nested browsing context</span>
      <li><span class="dfn-paneled" id="73317570">origin</span>
@@ -1836,13 +2043,16 @@ <h3 class="no-num no-ref heading settled" id="index-defined-elsewhere"><span cla
      <li><span class="dfn-paneled" id="2c543ae5">padding area</span>
      <li><span class="dfn-paneled" id="b1242144">padding edge</span>
      <li><span class="dfn-paneled" id="dddc4776">pinch zoom</span>
+     <li><span class="dfn-paneled" id="8daf6e87">post-multiplied</span>
      <li><span class="dfn-paneled" id="9a517a7d">queue a task</span>
      <li><span class="dfn-paneled" id="9c4c1e66">relevant settings object</span>
      <li><span class="dfn-paneled" id="04e154c5">report the exception</span>
+     <li><span class="dfn-paneled" id="2e8bd053">serialization</span>
      <li><span class="dfn-paneled" id="604e2d49">throw</span>
      <li><span class="dfn-paneled" id="4ce01aab">time origin</span>
      <li><span class="dfn-paneled" id="90f31f6c">top-level browsing context</span>
      <li><span class="dfn-paneled" id="c63519ed">top-level origin</span>
+     <li><span class="dfn-paneled" id="c2544db0">transformation matrix</span>
      <li><span class="dfn-paneled" id="db6ab50a">undefined</span>
      <li><span class="dfn-paneled" id="f3aafb20">viewport</span>
     </ul>
@@ -1909,6 +2119,7 @@ <h3 class="no-num no-ref heading settled" id="index-defined-elsewhere"><span cla
      <li><span class="dfn-paneled" id="889e932f">Exposed</span>
      <li><span class="dfn-paneled" id="dcf5fafa">FrozenArray</span>
      <li><span class="dfn-paneled" id="5372cca8">boolean</span>
+     <li><span class="dfn-paneled" id="f8de33a3">long</span>
      <li><span class="dfn-paneled" id="9cce47fd">sequence</span>
     </ul>
   </ul>
@@ -1950,6 +2161,8 @@ <h2 class="no-num no-ref heading settled" id="idl-index"><span class="content">I
   <c- b>readonly</c-> <c- b>attribute</c-> <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-DOMString"><c- b>DOMString</c-></a> <a class="idl-code" data-link-type="attribute" data-readonly data-type="DOMString" href="#dom-intersectionobserver-rootmargin"><c- g>rootMargin</c-></a>;
   <c- b>readonly</c-> <c- b>attribute</c-> <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-DOMString"><c- b>DOMString</c-></a> <a class="idl-code" data-link-type="attribute" data-readonly data-type="DOMString" href="#dom-intersectionobserver-scrollmargin"><c- g>scrollMargin</c-></a>;
   <c- b>readonly</c-> <c- b>attribute</c-> <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-frozen-array"><c- b>FrozenArray</c-></a>&lt;<a class="idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-double"><c- b>double</c-></a>> <a class="idl-code" data-link-type="attribute" data-readonly data-type="FrozenArray<double>" href="#dom-intersectionobserver-thresholds"><c- g>thresholds</c-></a>;
+  <c- b>readonly</c-> <c- b>attribute</c-> <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-long"><c- b>long</c-></a> <a class="idl-code" data-link-type="attribute" data-readonly data-type="long" href="#dom-intersectionobserver-delay"><c- g>delay</c-></a>;
+  <c- b>readonly</c-> <c- b>attribute</c-> <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-boolean"><c- b>boolean</c-></a> <a class="idl-code" data-link-type="attribute" data-readonly data-type="boolean" href="#dom-intersectionobserver-trackvisibility"><c- g>trackVisibility</c-></a>;
   <a class="idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-undefined"><c- b>undefined</c-></a> <a class="idl-code" data-link-type="method" href="#dom-intersectionobserver-observe"><c- g>observe</c-></a>(<a data-link-type="idl-name" href="https://dom.spec.whatwg.org/#element"><c- n>Element</c-></a> <a href="#dom-intersectionobserver-observe-target-target"><code><c- g>target</c-></code></a>);
   <a class="idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-undefined"><c- b>undefined</c-></a> <a class="idl-code" data-link-type="method" href="#dom-intersectionobserver-unobserve"><c- g>unobserve</c-></a>(<a data-link-type="idl-name" href="https://dom.spec.whatwg.org/#element"><c- n>Element</c-></a> <a href="#dom-intersectionobserver-unobserve-target-target"><code><c- g>target</c-></code></a>);
   <a class="idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-undefined"><c- b>undefined</c-></a> <a class="idl-code" data-link-type="method" href="#dom-intersectionobserver-disconnect"><c- g>disconnect</c-></a>();
@@ -1964,25 +2177,29 @@ <h2 class="no-num no-ref heading settled" id="idl-index"><span class="content">I
   <c- b>readonly</c-> <c- b>attribute</c-> <a data-link-type="idl-name" href="https://drafts.fxtf.org/geometry-1/#domrectreadonly"><c- n>DOMRectReadOnly</c-></a> <a class="idl-code" data-link-type="attribute" data-readonly data-type="DOMRectReadOnly" href="#dom-intersectionobserverentry-boundingclientrect"><c- g>boundingClientRect</c-></a>;
   <c- b>readonly</c-> <c- b>attribute</c-> <a data-link-type="idl-name" href="https://drafts.fxtf.org/geometry-1/#domrectreadonly"><c- n>DOMRectReadOnly</c-></a> <a class="idl-code" data-link-type="attribute" data-readonly data-type="DOMRectReadOnly" href="#dom-intersectionobserverentry-intersectionrect"><c- g>intersectionRect</c-></a>;
   <c- b>readonly</c-> <c- b>attribute</c-> <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-boolean"><c- b>boolean</c-></a> <a class="idl-code" data-link-type="attribute" data-readonly data-type="boolean" href="#dom-intersectionobserverentry-isintersecting"><c- g>isIntersecting</c-></a>;
+  <c- b>readonly</c-> <c- b>attribute</c-> <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-boolean"><c- b>boolean</c-></a> <a class="idl-code" data-link-type="attribute" data-readonly data-type="boolean" href="#dom-intersectionobserverentry-isvisible"><c- g>isVisible</c-></a>;
   <c- b>readonly</c-> <c- b>attribute</c-> <a class="idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-double"><c- b>double</c-></a> <a class="idl-code" data-link-type="attribute" data-readonly data-type="double" href="#dom-intersectionobserverentry-intersectionratio"><c- g>intersectionRatio</c-></a>;
   <c- b>readonly</c-> <c- b>attribute</c-> <a data-link-type="idl-name" href="https://dom.spec.whatwg.org/#element"><c- n>Element</c-></a> <a class="idl-code" data-link-type="attribute" data-readonly data-type="Element" href="#dom-intersectionobserverentry-target"><c- g>target</c-></a>;
 };
 
 <c- b>dictionary</c-> <a href="#dictdef-intersectionobserverentryinit"><code><c- g>IntersectionObserverEntryInit</c-></code></a> {
-  <c- b>required</c-> <a data-link-type="idl-name" href="http://www.w3.org/TR/hr-time/#domhighrestimestamp"><c- n>DOMHighResTimeStamp</c-></a> <a data-type="DOMHighResTimeStamp " href="#dom-intersectionobserverentryinit-time"><code><c- g>time</c-></code></a>;
-  <c- b>required</c-> <a data-link-type="idl-name" href="https://drafts.fxtf.org/geometry-1/#dictdef-domrectinit"><c- n>DOMRectInit</c-></a>? <a data-type="DOMRectInit? " href="#dom-intersectionobserverentryinit-rootbounds"><code><c- g>rootBounds</c-></code></a>;
-  <c- b>required</c-> <a data-link-type="idl-name" href="https://drafts.fxtf.org/geometry-1/#dictdef-domrectinit"><c- n>DOMRectInit</c-></a> <a data-type="DOMRectInit " href="#dom-intersectionobserverentryinit-boundingclientrect"><code><c- g>boundingClientRect</c-></code></a>;
-  <c- b>required</c-> <a data-link-type="idl-name" href="https://drafts.fxtf.org/geometry-1/#dictdef-domrectinit"><c- n>DOMRectInit</c-></a> <a data-type="DOMRectInit " href="#dom-intersectionobserverentryinit-intersectionrect"><code><c- g>intersectionRect</c-></code></a>;
-  <c- b>required</c-> <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-boolean"><c- b>boolean</c-></a> <a data-type="boolean " href="#dom-intersectionobserverentryinit-isintersecting"><code><c- g>isIntersecting</c-></code></a>;
-  <c- b>required</c-> <a class="idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-double"><c- b>double</c-></a> <a data-type="double " href="#dom-intersectionobserverentryinit-intersectionratio"><code><c- g>intersectionRatio</c-></code></a>;
-  <c- b>required</c-> <a data-link-type="idl-name" href="https://dom.spec.whatwg.org/#element"><c- n>Element</c-></a> <a data-type="Element " href="#dom-intersectionobserverentryinit-target"><code><c- g>target</c-></code></a>;
+  <c- b>required</c-> <a data-link-type="idl-name" href="http://www.w3.org/TR/hr-time/#domhighrestimestamp"><c- n>DOMHighResTimeStamp</c-></a> <a data-type="DOMHighResTimeStamp" href="#dom-intersectionobserverentryinit-time"><code><c- g>time</c-></code></a>;
+  <c- b>required</c-> <a data-link-type="idl-name" href="https://drafts.fxtf.org/geometry-1/#dictdef-domrectinit"><c- n>DOMRectInit</c-></a>? <a data-type="DOMRectInit?" href="#dom-intersectionobserverentryinit-rootbounds"><code><c- g>rootBounds</c-></code></a>;
+  <c- b>required</c-> <a data-link-type="idl-name" href="https://drafts.fxtf.org/geometry-1/#dictdef-domrectinit"><c- n>DOMRectInit</c-></a> <a data-type="DOMRectInit" href="#dom-intersectionobserverentryinit-boundingclientrect"><code><c- g>boundingClientRect</c-></code></a>;
+  <c- b>required</c-> <a data-link-type="idl-name" href="https://drafts.fxtf.org/geometry-1/#dictdef-domrectinit"><c- n>DOMRectInit</c-></a> <a data-type="DOMRectInit" href="#dom-intersectionobserverentryinit-intersectionrect"><code><c- g>intersectionRect</c-></code></a>;
+  <c- b>required</c-> <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-boolean"><c- b>boolean</c-></a> <a data-type="boolean" href="#dom-intersectionobserverentryinit-isintersecting"><code><c- g>isIntersecting</c-></code></a>;
+  <c- b>required</c-> <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-boolean"><c- b>boolean</c-></a> <a data-type="boolean" href="#dom-intersectionobserverentryinit-isvisible"><code><c- g>isVisible</c-></code></a>;
+  <c- b>required</c-> <a class="idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-double"><c- b>double</c-></a> <a data-type="double" href="#dom-intersectionobserverentryinit-intersectionratio"><code><c- g>intersectionRatio</c-></code></a>;
+  <c- b>required</c-> <a data-link-type="idl-name" href="https://dom.spec.whatwg.org/#element"><c- n>Element</c-></a> <a data-type="Element" href="#dom-intersectionobserverentryinit-target"><code><c- g>target</c-></code></a>;
 };
 
 <c- b>dictionary</c-> <a href="#dictdef-intersectionobserverinit"><code><c- g>IntersectionObserverInit</c-></code></a> {
-  (<a data-link-type="idl-name" href="https://dom.spec.whatwg.org/#element"><c- n>Element</c-></a> <c- b>or</c-> <a data-link-type="idl-name" href="https://dom.spec.whatwg.org/#document"><c- n>Document</c-></a>)?  <a class="idl-code" data-default="null" data-link-type="dict-member" data-type="(Element or Document)?  " href="#dom-intersectionobserverinit-root"><c- g>root</c-></a> = <c- b>null</c->;
-  <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-DOMString"><c- b>DOMString</c-></a> <a class="idl-code" data-default="&quot;0px&quot;" data-link-type="dict-member" data-type="DOMString " href="#dom-intersectionobserverinit-rootmargin"><c- g>rootMargin</c-></a> = "0px";
-  <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-DOMString"><c- b>DOMString</c-></a> <a class="idl-code" data-default="&quot;0px&quot;" data-link-type="dict-member" data-type="DOMString " href="#dom-intersectionobserverinit-scrollmargin"><c- g>scrollMargin</c-></a> = "0px";
-  (<a class="idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-double"><c- b>double</c-></a> <c- b>or</c-> <a data-link-type="dfn" href="https://webidl.spec.whatwg.org/#idl-sequence"><c- b>sequence</c-></a>&lt;<a class="idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-double"><c- b>double</c-></a>>) <a class="idl-code" data-default="0" data-link-type="dict-member" data-type="(double or sequence<double>) " href="#dom-intersectionobserverinit-threshold"><c- g>threshold</c-></a> = 0;
+  (<a data-link-type="idl-name" href="https://dom.spec.whatwg.org/#element"><c- n>Element</c-></a> <c- b>or</c-> <a data-link-type="idl-name" href="https://dom.spec.whatwg.org/#document"><c- n>Document</c-></a>)?  <a class="idl-code" data-default="null" data-link-type="dict-member" data-type="(Element or Document)?" href="#dom-intersectionobserverinit-root"><c- g>root</c-></a> = <c- b>null</c->;
+  <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-DOMString"><c- b>DOMString</c-></a> <a class="idl-code" data-default="&quot;0px&quot;" data-link-type="dict-member" data-type="DOMString" href="#dom-intersectionobserverinit-rootmargin"><c- g>rootMargin</c-></a> = "0px";
+  <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-DOMString"><c- b>DOMString</c-></a> <a class="idl-code" data-default="&quot;0px&quot;" data-link-type="dict-member" data-type="DOMString" href="#dom-intersectionobserverinit-scrollmargin"><c- g>scrollMargin</c-></a> = "0px";
+  (<a class="idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-double"><c- b>double</c-></a> <c- b>or</c-> <a data-link-type="dfn" href="https://webidl.spec.whatwg.org/#idl-sequence"><c- b>sequence</c-></a>&lt;<a class="idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-double"><c- b>double</c-></a>>) <a class="idl-code" data-default="0" data-link-type="dict-member" data-type="(double or sequence<double>)" href="#dom-intersectionobserverinit-threshold"><c- g>threshold</c-></a> = 0;
+  <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-long"><c- b>long</c-></a> <a class="idl-code" data-default="0" data-link-type="dict-member" data-type="long" href="#dom-intersectionobserverinit-delay"><c- g>delay</c-></a> = 0;
+  <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-boolean"><c- b>boolean</c-></a> <a class="idl-code" data-default="false" data-link-type="dict-member" data-type="boolean" href="#dom-intersectionobserverinit-trackvisibility"><c- g>trackVisibility</c-></a> = <c- b>false</c->;
 };
 
 </pre>
@@ -2258,429 +2475,8 @@ <h2 class="no-num no-ref heading settled" id="idl-index"><span class="content">I
     </div>
    </div>
   </details>
-<script>/* Boilerplate: script-dfn-panel */
-"use strict";
-{
-    const dfnsJson = window.dfnsJson || {};
-
-    function genDfnPanel({dfnID, url, dfnText, refSections, external}) {
-        return mk.aside({
-            class: "dfn-panel",
-            id: `infopanel-for-${dfnID}`,
-            "data-for": dfnID,
-            "aria-labelled-by":`infopaneltitle-for-${dfnID}`,
-            },
-            mk.span({id:`infopaneltitle-for-${dfnID}`, style:"display:none"},
-                `Info about the '${dfnText}' ${external?"external":""} reference.`),
-            mk.a({href:url}, url),
-            mk.b({}, "Referenced in:"),
-            mk.ul({},
-                ...refSections.map(section=>
-                    mk.li({},
-                        ...section.refs.map((ref, refI)=>
-                            [
-                                mk.a({
-                                    href: `#${ref.id}`
-                                    },
-                                    (refI == 0) ? section.title : `(${refI + 1})`
-                                ),
-                                " ",
-                            ]
-                        ),
-                    ),
-                ),
-            ),
-        );
-    }
-
-    function genAllDfnPanels() {
-        for(const panelData of Object.values(window.dfnpanelData)) {
-            const dfnID = panelData.dfnID;
-            const dfn = document.getElementById(dfnID);
-            if(!dfn) {
-                console.log(`Can't find dfn#${dfnID}.`, panelData);
-            } else {
-                const panel = genDfnPanel(panelData);
-                append(document.body, panel);
-                insertDfnPopupAction(dfn, panel)
-            }
-        }
-    }
-
-    document.addEventListener("DOMContentLoaded", ()=>{
-        genAllDfnPanels();
-
-        // Add popup behavior to all dfns to show the corresponding dfn-panel.
-        var dfns = queryAll('.dfn-paneled');
-        for(let dfn of dfns) { ; }
-
-        document.body.addEventListener("click", (e) => {
-            // If not handled already, just hide all dfn panels.
-            hideAllDfnPanels();
-        });
-    })
-
-
-    function hideAllDfnPanels() {
-        // Turn off any currently "on" or "activated" panels.
-        queryAll(".dfn-panel.on, .dfn-panel.activated").forEach(el=>hideDfnPanel(el));
-    }
-
-    function showDfnPanel(dfnPanel, dfn) {
-        hideAllDfnPanels(); // Only display one at this time.
-        dfn.setAttribute("aria-expanded", "true");
-        dfnPanel.classList.add("on");
-        dfnPanel.style.left = "5px";
-        dfnPanel.style.top = "0px";
-        const panelRect = dfnPanel.getBoundingClientRect();
-        const panelWidth = panelRect.right - panelRect.left;
-        if (panelRect.right > document.body.scrollWidth) {
-            // Panel's overflowing the screen.
-            // Just drop it below the dfn and flip it rightward instead.
-            // This still wont' fix things if the screen is *really* wide,
-            // but fixing that's a lot harder without 'anchor()'.
-            dfnPanel.style.top = "1.5em";
-            dfnPanel.style.left = "auto";
-            dfnPanel.style.right = "0px";
-        }
-    }
-
-    function pinDfnPanel(dfnPanel) {
-        // Switch it to "activated" state, which pins it.
-        dfnPanel.classList.add("activated");
-        dfnPanel.style.left = null;
-        dfnPanel.style.top = null;
-    }
-
-    function hideDfnPanel(dfnPanel, dfn) {
-        if(!dfn) {
-            dfn = document.getElementById(dfnPanel.getAttribute("data-for"));
-        }
-        dfn.setAttribute("aria-expanded", "false")
-        dfnPanel.classList.remove("on");
-        dfnPanel.classList.remove("activated");
-    }
-
-    function toggleDfnPanel(dfnPanel, dfn) {
-        if(dfnPanel.classList.contains("on")) {
-            hideDfnPanel(dfnPanel, dfn);
-        } else {
-            showDfnPanel(dfnPanel, dfn);
-        }
-    }
-
-    function insertDfnPopupAction(dfn, dfnPanel) {
-        // Find dfn panel
-        const panelWrapper = document.createElement('span');
-        panelWrapper.appendChild(dfnPanel);
-        panelWrapper.style.position = "relative";
-        panelWrapper.style.height = "0px";
-        dfn.insertAdjacentElement("afterend", panelWrapper);
-        dfn.setAttribute('role', 'button');
-        dfn.setAttribute('aria-expanded', 'false')
-        dfn.tabIndex = 0;
-        dfn.classList.add('has-dfn-panel');
-        dfn.addEventListener('click', (event) => {
-            showDfnPanel(dfnPanel, dfn);
-            event.stopPropagation();
-        });
-        dfn.addEventListener('keypress', (event) => {
-            const kc = event.keyCode;
-            // 32->Space, 13->Enter
-            if(kc == 32 || kc == 13) {
-                toggleDfnPanel(dfnPanel, dfn);
-                event.stopPropagation();
-                event.preventDefault();
-            }
-        });
-
-        dfnPanel.addEventListener('click', (event) => {
-            if (event.target.nodeName == 'A') {
-                pinDfnPanel(dfnPanel);
-            }
-            event.stopPropagation();
-        });
-
-        dfnPanel.addEventListener('keydown', (event) => {
-            if(event.keyCode == 27) { // Escape key
-                hideDfnPanel(dfnPanel, dfn);
-                event.stopPropagation();
-                event.preventDefault();
-            }
-        })
-    }
-}
-</script>
-<script>/* Boilerplate: script-dfn-panel */
-"use strict";
-{
-    const dfnsJson = window.dfnsJson || {};
-
-    function genDfnPanel({dfnID, url, dfnText, refSections, external}) {
-        return mk.aside({
-            class: "dfn-panel",
-            id: `infopanel-for-${dfnID}`,
-            "data-for": dfnID,
-            "aria-labelled-by":`infopaneltitle-for-${dfnID}`,
-            },
-            mk.span({id:`infopaneltitle-for-${dfnID}`, style:"display:none"},
-                `Info about the '${dfnText}' ${external?"external":""} reference.`),
-            mk.a({href:url}, url),
-            mk.b({}, "Referenced in:"),
-            mk.ul({},
-                ...refSections.map(section=>
-                    mk.li({},
-                        ...section.refs.map((ref, refI)=>
-                            [
-                                mk.a({
-                                    href: `#${ref.id}`
-                                    },
-                                    (refI == 0) ? section.title : `(${refI + 1})`
-                                ),
-                                " ",
-                            ]
-                        ),
-                    ),
-                ),
-            ),
-        );
-    }
-
-    function genAllDfnPanels() {
-        for(const panelData of Object.values(window.dfnpanelData)) {
-            const dfnID = panelData.dfnID;
-            const dfn = document.getElementById(dfnID);
-            if(!dfn) {
-                console.log(`Can't find dfn#${dfnID}.`, panelData);
-            } else {
-                const panel = genDfnPanel(panelData);
-                append(document.body, panel);
-                insertDfnPopupAction(dfn, panel)
-            }
-        }
-    }
-
-    document.addEventListener("DOMContentLoaded", ()=>{
-        genAllDfnPanels();
-
-        // Add popup behavior to all dfns to show the corresponding dfn-panel.
-        var dfns = queryAll('.dfn-paneled');
-        for(let dfn of dfns) { ; }
-
-        document.body.addEventListener("click", (e) => {
-            // If not handled already, just hide all dfn panels.
-            hideAllDfnPanels();
-        });
-    })
-
-
-    function hideAllDfnPanels() {
-        // Turn off any currently "on" or "activated" panels.
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+document.addEventListener("DOMContentLoaded", ()=>{
+    genAllDfnPanels();
+
+    document.body.addEventListener("click", (e) => {
+        // If not handled already, just hide all dfn panels.
+        hideAllDfnPanels();
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+});
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+window.addEventListener("resize", () => {
+    // Pin any visible dfn panel
+    queryAll(".dfn-panel.on, .dfn-panel.activated").forEach(el=>positionDfnPanel(el));
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+function genAllDfnPanels() {
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+}
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+function genDfnPanel(dfn, { dfnID, url, dfnText, refSections, external }) {
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+        "aria-labelled-by":`infopaneltitle-for-${dfnID}`,
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+            `Info about the '${dfnText}' ${external?"external":""} reference.`),
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+                    mk.li({},
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+                                mk.a({ href: `#${ref.id}` },
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+                                ),
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+    dfnPanel.addEventListener('click', (event) => {
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+            scrollToTargetAndHighlight(event);
+            pinDfnPanel(dfnPanel);
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+    dfnPanel.dfn = dfn;
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+}
+
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+function hideAllDfnPanels() {
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+    queryAll(".dfn-panel").forEach(dfnPanel=>hideDfnPanel({dfnPanel}));
+}
+
+function showDfnPanel(dfn) {
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+
+    dfn.setAttribute("aria-expanded", "true");
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+    const dfnPanel = genDfnPanel(dfn, dfn.panelData);
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+    // Give the dfn a unique tabindex, and then
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+}
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+}
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+function pinDfnPanel(dfnPanel) {
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+function hideDfnPanel({dfn, dfnPanel}) {
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+function toggleDfnPanel(dfn) {
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+}
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+function insertDfnPopupAction(dfn) {
+    dfn.setAttribute('role', 'button');
+    dfn.setAttribute('aria-expanded', 'false')
+    dfn.tabIndex = 0;
+    dfn.classList.add('has-dfn-panel');
+    dfn.addEventListener('click', (event) => {
+        toggleDfnPanel(dfn);
+        event.stopPropagation();
+    });
+    dfn.addEventListener('keypress', (event) => {
+        const kc = event.keyCode;
+        // 32->Space, 13->Enter
+        if(kc == 32 || kc == 13) {
+            toggleDfnPanel(dfn);
+            event.stopPropagation();
+            event.preventDefault();
+        }
+    });
+}
+
+function refocusOnTarget(event) {
+    const target = event.target;
+    setTimeout(() => {
+        // Refocus on the event.target element.
+        // This is needed after browser scrolls to the destination.
+        target.focus();
+    });
+}
+
+// TODO: shared util
+// Returns the root-level absolute position {left and top} of element.
+function getBounds(el, relativeTo=document.body) {
+    const relativeRect = relativeTo.getBoundingClientRect();
+    const elRect = el.getBoundingClientRect();
+    const top = elRect.top - relativeRect.top;
+    const left = elRect.left - relativeRect.left;
+    return {
+        top,
+        left,
+        bottom: top + elRect.height,
+        right: left + elRect.width,
+    }
+}
+
+function scrollToTargetAndHighlight(event) {
+    let hash = event.target.hash;
+    if (hash) {
+        hash = decodeURIComponent(hash.substring(1));
+        const dest = document.getElementById(hash);
+        if (dest) {
+            dest.classList.add('highlighted');
+            setTimeout(() => dest.classList.remove('highlighted'), 1000);
+        }
+    }
+}
+
+// Functions, divided by link type, that wrap an autolink's
+// contents with the appropriate outer syntax.
+// Alternately, a string naming another type they format
+// the same as.
+function needsFor(type) {
+    switch(type) {
+        case "descriptor":
+        case "value":
+        case "element-attr":
+        case "attr-value":
+        case "element-state":
+        case "method":
+        case "constructor":
+        case "argument":
+        case "attribute":
+        case "const":
+        case "dict-member":
+        case "event":
+        case "enum-value":
+        case "stringifier":
+        case "serializer":
+        case "iterator":
+        case "maplike":
+        case "setlike":
+        case "state":
+        case "mode":
+        case "context":
+        case "facet": return true;
+
+        default: return false;
+    }
+}
+function refusesFor(type) {
+    switch(type) {
+        case "property":
+        case "element":
+        case "interface":
+        case "namespace":
+        case "callback":
+        case "dictionary":
+        case "enum":
+        case "exception":
+        case "typedef":
+        case "http-header":
+        case "permission": return true;
+
+        default: return false;
+    }
+}
+function linkFormatterFromType(type) {
+    switch(type) {
+        case 'scheme':
+        case 'permission':
+        case 'dfn': return (text) => `[=${text}=]`;
+
+        case 'abstract-op': return (text) => `[\$${text}\$]`;
+
+        case 'function':
+        case 'at-rule':
+        case 'selector':
+        case 'value': return (text) => `''${text}''`;
+
+        case 'http-header': return (text) => `[:${text}:]`;
+
+        case 'interface':
+        case 'constructor':
+        case 'method':
+        case 'argument':
+        case 'attribute':
+        case 'callback':
+        case 'dictionary':
+        case 'dict-member':
+        case 'enum':
+        case 'enum-value':
+        case 'exception':
+        case 'const':
+        case 'typedef':
+        case 'stringifier':
+        case 'serializer':
+        case 'iterator':
+        case 'maplike':
+        case 'setlike':
+        case 'extended-attribute':
+        case 'event':
+        case 'idl': return (text) => `{{${text}}}`;
+
+        case 'element-state':
+        case 'element-attr':
+        case 'attr-value':
+        case 'element': return (element) => `<{${element}}>`;
+
+        case 'grammar': return (text) => `${text} (within a <pre class=prod>)`;
+
+        case 'type': return (text)=> `<<${text}>>`;
+
+        case 'descriptor':
+        case 'property': return (text) => `'${text}'`;
+
+        default: return;
+    };
+};
+
+function genLinkingSyntaxes(dfn) {
+    if(dfn.tagName != "DFN") return;
+
+    const type = dfn.getAttribute('data-dfn-type');
+    if(!type) {
+        console.log(`<dfn> doesn't have a data-dfn-type:`, dfn);
+        return [];
+    }
+
+    // Return a function that wraps link text based on the type
+    const linkFormatter = linkFormatterFromType(type);
+    if(!linkFormatter) {
+        console.log(`<dfn> has an unknown data-dfn-type:`, dfn);
+        return [];
+    }
+
+    let ltAlts;
+    if(dfn.hasAttribute('data-lt')) {
+        ltAlts = dfn.getAttribute('data-lt')
+            .split("|")
+            .map(x=>x.trim());
+    } else {
+        ltAlts = [dfn.textContent.trim()];
+    }
+    if(type == "type") {
+        // lt of "<foo>", but "foo" is the interior;
+        // <<foo/bar>> is how you write it with a for,
+        // not <foo/<bar>> or whatever.
+        for(var i = 0; i < ltAlts.length; i++) {
+            const lt = ltAlts[i];
+            const match = /<(.*)>/.exec(lt);
+            if(match) { ltAlts[i] = match[1]; }
+        }
+    }
+
+    let forAlts;
+    if(dfn.hasAttribute('data-dfn-for')) {
+        forAlts = dfn.getAttribute('data-dfn-for')
+            .split(",")
+            .map(x=>x.trim());
+    } else {
+        forAlts = [''];
+    }
+
+    let linkingSyntaxes = [];
+    if(!needsFor(type)) {
+        for(const lt of ltAlts) {
+            linkingSyntaxes.push(linkFormatter(lt));
+        }
+    }
+    if(!refusesFor(type)) {
+        for(const f of forAlts) {
+            linkingSyntaxes.push(linkFormatter(`${f}/${ltAlts[0]}`))
+        }
+    }
+    return [
+        mk.b({}, 'Possible linking syntaxes:'),
+        mk.ul({},
+            ...linkingSyntaxes.map(link => {
+                const copyLink = async () =>
+                    await navigator.clipboard.writeText(link);
+                return mk.li({},
+                    mk.div({ class: 'link-item' },
+                        mk.button({
+                            class: 'copy-icon', title: 'Copy',
+                            type: 'button',
+                            _onclick: copyLink,
+                            tabindex: 0,
+                        }, mk.span({ class: 'icon' }) ),
+                        mk.span({}, link)
+                    )
+                );
+            })
+        )
+    ];
+}
 }
 </script>
 <script>/* Boilerplate: script-position-annos */
 "use strict";
 {
-
 function repositionAnnoPanels(){
     const panels = [...document.querySelectorAll("[data-anno-for]")];
+    hydratePanels(panels);
+    let vSoFar = 0;
+    for(const panel of panels.sort(cmpTops)) {
+        if(panel.top < vSoFar) {
+            panel.top = vSoFar;
+            panel.style.top = vSoFar + "px";
+        }
+        vSoFar = panel.top + panel.height + 15;
+    }
+}
+function hydratePanels(panels) {
     const main = document.querySelector("main");
     let mainRect;
     if(main) mainRect = main.getBoundingClientRect();
+    // First display them all, if they're not already visible.
+    for(const panel of panels) {
+        panel.classList.remove("unpositioned");
+    }
+    // Measure them all
     for(const panel of panels) {
         const dfn = document.getElementById(panel.getAttribute("data-anno-for"));
         if(!dfn) {
             console.log("Can't find the annotation panel target:", panel);
             continue;
         }
-        const rect = dfn.getBoundingClientRect();
-        const top = window.scrollY + rect.top
-        panel.style.top = top + "px";
-        panel.top = top;
-        panel.height = rect.height;
-        panel.classList.remove("unpositioned");
-        const panelRect = panel.getBoundingClientRect()
+        panel.dfn = dfn;
+        panel.top = window.scrollY + dfn.getBoundingClientRect().top;
+        let panelRect = panel.getBoundingClientRect();
+        panel.height = panelRect.height;
         if(main) {
-            panel.classList.toggle("overlapping-main", panelRect.left < mainRect.right)
+            panel.overlappingMain = panelRect.left < mainRect.right;
+        } else {
+            panel.overlappingMain = false;
         }
     }
-    let vSoFar = 0;
-    for(const panel of panels.sort(cmpTops)) {
-        if(panel.top < vSoFar) {
-            panel.top = vSoFar;
-            panel.style.top = vSoFar + "px";
-        }
-        vSoFar = panel.top + panel.height + 15;
+    // And finally position them
+    for(const panel of panels) {
+        const dfn = panel.dfn;
+        if(!dfn) continue;
+        panel.style.top = panel.top + "px";
+        panel.classList.toggle("overlapping-main", panel.overlappingMain);
     }
 }
 
@@ -2919,4 +3265,334 @@ <h2 class="no-num no-ref heading settled" id="idl-index"><span class="content">I
 window.addEventListener("load", repositionAnnoPanels);
 window.addEventListener("resize", repositionAnnoPanels);
 }
+</script>
+<script>/* Boilerplate: script-ref-hints */
+"use strict";
+{
+let refsData = {
+"#apply-scroll-margin-to-a-scrollport": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"apply scroll margin to a scrollport","type":"dfn","url":"#apply-scroll-margin-to-a-scrollport"},
+"#callbackdef-intersectionobservercallback": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"IntersectionObserverCallback","type":"callback","url":"#callbackdef-intersectionobservercallback"},
+"#compute-the-intersection": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"compute the intersection","type":"dfn","url":"#compute-the-intersection"},
+"#dictdef-intersectionobserverentryinit": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"IntersectionObserverEntryInit","type":"dictionary","url":"#dictdef-intersectionobserverentryinit"},
+"#dictdef-intersectionobserverinit": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"IntersectionObserverInit","type":"dictionary","url":"#dictdef-intersectionobserverinit"},
+"#document-intersectionobservertaskqueued": {"export":true,"for_":["Document"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"intersectionobservertaskqueued","type":"dfn","url":"#document-intersectionobservertaskqueued"},
+"#dom-element-registeredintersectionobservers-slot": {"export":true,"for_":["Element"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"[[RegisteredIntersectionObservers]]","type":"attribute","url":"#dom-element-registeredintersectionobservers-slot"},
+"#dom-intersectionobserver-callback-slot": {"export":true,"for_":["IntersectionObserver"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"[[callback]]","type":"attribute","url":"#dom-intersectionobserver-callback-slot"},
+"#dom-intersectionobserver-delay": {"export":true,"for_":["IntersectionObserver"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"delay","type":"attribute","url":"#dom-intersectionobserver-delay"},
+"#dom-intersectionobserver-delay-slot": {"export":true,"for_":["IntersectionObserver"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"[[delay]]","type":"attribute","url":"#dom-intersectionobserver-delay-slot"},
+"#dom-intersectionobserver-disconnect": {"export":true,"for_":["IntersectionObserver"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"disconnect()","type":"method","url":"#dom-intersectionobserver-disconnect"},
+"#dom-intersectionobserver-intersectionobserver": {"export":true,"for_":["IntersectionObserver"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"IntersectionObserver(callback, options)","type":"constructor","url":"#dom-intersectionobserver-intersectionobserver"},
+"#dom-intersectionobserver-observationtargets-slot": {"export":true,"for_":["IntersectionObserver"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"[[ObservationTargets]]","type":"attribute","url":"#dom-intersectionobserver-observationtargets-slot"},
+"#dom-intersectionobserver-observe": {"export":true,"for_":["IntersectionObserver"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"observe(target)","type":"method","url":"#dom-intersectionobserver-observe"},
+"#dom-intersectionobserver-queuedentries-slot": {"export":true,"for_":["IntersectionObserver"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"[[QueuedEntries]]","type":"attribute","url":"#dom-intersectionobserver-queuedentries-slot"},
+"#dom-intersectionobserver-root": {"export":true,"for_":["IntersectionObserver"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"root","type":"attribute","url":"#dom-intersectionobserver-root"},
+"#dom-intersectionobserver-rootmargin": {"export":true,"for_":["IntersectionObserver"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"rootMargin","type":"attribute","url":"#dom-intersectionobserver-rootmargin"},
+"#dom-intersectionobserver-rootmargin-slot": {"export":true,"for_":["IntersectionObserver"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"[[rootMargin]]","type":"attribute","url":"#dom-intersectionobserver-rootmargin-slot"},
+"#dom-intersectionobserver-scrollmargin": {"export":true,"for_":["IntersectionObserver"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"scrollMargin","type":"attribute","url":"#dom-intersectionobserver-scrollmargin"},
+"#dom-intersectionobserver-scrollmargin-slot": {"export":true,"for_":["IntersectionObserver"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"[[scrollMargin]]","type":"attribute","url":"#dom-intersectionobserver-scrollmargin-slot"},
+"#dom-intersectionobserver-takerecords": {"export":true,"for_":["IntersectionObserver"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"takeRecords()","type":"method","url":"#dom-intersectionobserver-takerecords"},
+"#dom-intersectionobserver-thresholds": {"export":true,"for_":["IntersectionObserver"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"thresholds","type":"attribute","url":"#dom-intersectionobserver-thresholds"},
+"#dom-intersectionobserver-trackvisibility": {"export":true,"for_":["IntersectionObserver"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"trackVisibility","type":"attribute","url":"#dom-intersectionobserver-trackvisibility"},
+"#dom-intersectionobserver-trackvisibility-slot": {"export":true,"for_":["IntersectionObserver"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"[[trackVisibility]]","type":"attribute","url":"#dom-intersectionobserver-trackvisibility-slot"},
+"#dom-intersectionobserver-unobserve": {"export":true,"for_":["IntersectionObserver"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"unobserve(target)","type":"method","url":"#dom-intersectionobserver-unobserve"},
+"#dom-intersectionobserverentry-boundingclientrect": {"export":true,"for_":["IntersectionObserverEntry"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"boundingClientRect","type":"attribute","url":"#dom-intersectionobserverentry-boundingclientrect"},
+"#dom-intersectionobserverentry-intersectionratio": {"export":true,"for_":["IntersectionObserverEntry"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"intersectionRatio","type":"attribute","url":"#dom-intersectionobserverentry-intersectionratio"},
+"#dom-intersectionobserverentry-intersectionrect": {"export":true,"for_":["IntersectionObserverEntry"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"intersectionRect","type":"attribute","url":"#dom-intersectionobserverentry-intersectionrect"},
+"#dom-intersectionobserverentry-isintersecting": {"export":true,"for_":["IntersectionObserverEntry"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"isIntersecting","type":"attribute","url":"#dom-intersectionobserverentry-isintersecting"},
+"#dom-intersectionobserverentry-isvisible": {"export":true,"for_":["IntersectionObserverEntry"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"isVisible","type":"attribute","url":"#dom-intersectionobserverentry-isvisible"},
+"#dom-intersectionobserverentry-rootbounds": {"export":true,"for_":["IntersectionObserverEntry"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"rootBounds","type":"attribute","url":"#dom-intersectionobserverentry-rootbounds"},
+"#dom-intersectionobserverentry-target": {"export":true,"for_":["IntersectionObserverEntry"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"target","type":"attribute","url":"#dom-intersectionobserverentry-target"},
+"#dom-intersectionobserverentry-time": {"export":true,"for_":["IntersectionObserverEntry"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"time","type":"attribute","url":"#dom-intersectionobserverentry-time"},
+"#dom-intersectionobserverinit-delay": {"export":true,"for_":["IntersectionObserverInit"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"delay","type":"dict-member","url":"#dom-intersectionobserverinit-delay"},
+"#dom-intersectionobserverinit-root": {"export":true,"for_":["IntersectionObserverInit"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"root","type":"dict-member","url":"#dom-intersectionobserverinit-root"},
+"#dom-intersectionobserverinit-rootmargin": {"export":true,"for_":["IntersectionObserverInit"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"rootMargin","type":"dict-member","url":"#dom-intersectionobserverinit-rootmargin"},
+"#dom-intersectionobserverinit-scrollmargin": {"export":true,"for_":["IntersectionObserverInit"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"scrollMargin","type":"dict-member","url":"#dom-intersectionobserverinit-scrollmargin"},
+"#dom-intersectionobserverinit-threshold": {"export":true,"for_":["IntersectionObserverInit"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"threshold","type":"dict-member","url":"#dom-intersectionobserverinit-threshold"},
+"#dom-intersectionobserverinit-trackvisibility": {"export":true,"for_":["IntersectionObserverInit"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"trackVisibility","type":"dict-member","url":"#dom-intersectionobserverinit-trackvisibility"},
+"#dom-intersectionobserverregistration-lastupdatetime": {"export":true,"for_":["IntersectionObserverRegistration"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"lastUpdateTime","type":"attribute","url":"#dom-intersectionobserverregistration-lastupdatetime"},
+"#dom-intersectionobserverregistration-observer": {"export":true,"for_":["IntersectionObserverRegistration"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"observer","type":"attribute","url":"#dom-intersectionobserverregistration-observer"},
+"#dom-intersectionobserverregistration-previousisintersecting": {"export":true,"for_":["IntersectionObserverRegistration"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"previousIsIntersecting","type":"attribute","url":"#dom-intersectionobserverregistration-previousisintersecting"},
+"#dom-intersectionobserverregistration-previousisvisible": {"export":true,"for_":["IntersectionObserverRegistration"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"previousIsVisible","type":"attribute","url":"#dom-intersectionobserverregistration-previousisvisible"},
+"#dom-intersectionobserverregistration-previousthresholdindex": {"export":true,"for_":["IntersectionObserverRegistration"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"previousThresholdIndex","type":"attribute","url":"#dom-intersectionobserverregistration-previousthresholdindex"},
+"#effective-transformation-matrix": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"effective transformation matrix","type":"dfn","url":"#effective-transformation-matrix"},
+"#initialize-a-new-intersectionobserver": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"initialize a new intersectionobserver","type":"dfn","url":"#initialize-a-new-intersectionobserver"},
+"#intersection-observer": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"intersection observer","type":"dfn","url":"#intersection-observer"},
+"#intersection-observer-processing-model": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"processing model","type":"dfn","url":"#intersection-observer-processing-model"},
+"#intersectionobserver": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"IntersectionObserver","type":"interface","url":"#intersectionobserver"},
+"#intersectionobserver-content-clip": {"export":true,"for_":["IntersectionObserver"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"content clip","type":"dfn","url":"#intersectionobserver-content-clip"},
+"#intersectionobserver-cross-origin-domain-target": {"export":true,"for_":["IntersectionObserver"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"cross-origin-domain target","type":"dfn","url":"#intersectionobserver-cross-origin-domain-target"},
+"#intersectionobserver-explicit-root-observer": {"export":true,"for_":["IntersectionObserver"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"explicit root observer","type":"dfn","url":"#intersectionobserver-explicit-root-observer"},
+"#intersectionobserver-implicit-root": {"export":true,"for_":["IntersectionObserver"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"implicit root","type":"dfn","url":"#intersectionobserver-implicit-root"},
+"#intersectionobserver-implicit-root-observer": {"export":true,"for_":["IntersectionObserver"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"implicit root observer","type":"dfn","url":"#intersectionobserver-implicit-root-observer"},
+"#intersectionobserver-intersection-root": {"export":true,"for_":["IntersectionObserver"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"intersection root","type":"dfn","url":"#intersectionobserver-intersection-root"},
+"#intersectionobserver-root-intersection-rectangle": {"export":true,"for_":["IntersectionObserver"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"root intersection rectangle","type":"dfn","url":"#intersectionobserver-root-intersection-rectangle"},
+"#intersectionobserver-same-origin-domain-target": {"export":true,"for_":["IntersectionObserver"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"same-origin-domain target","type":"dfn","url":"#intersectionobserver-same-origin-domain-target"},
+"#intersectionobserver-target": {"export":true,"for_":["IntersectionObserver"],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"target","type":"dfn","url":"#intersectionobserver-target"},
+"#intersectionobserver-task-source": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"intersectionobserver task source","type":"dfn","url":"#intersectionobserver-task-source"},
+"#intersectionobserverentry": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"IntersectionObserverEntry","type":"interface","url":"#intersectionobserverentry"},
+"#intersectionobserverregistration": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"IntersectionObserverRegistration","type":"interface","url":"#intersectionobserverregistration"},
+"#notify-intersection-observers": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"notify intersection observers","type":"dfn","url":"#notify-intersection-observers"},
+"#observe-a-target-element": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"observe a target element","type":"dfn","url":"#observe-a-target-element"},
+"#parse-a-margin": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"parse a margin","type":"dfn","url":"#parse-a-margin"},
+"#pending-initial-intersectionobserver-targets": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"pending initial intersectionobserver targets","type":"dfn","url":"#pending-initial-intersectionobserver-targets"},
+"#queue-an-intersection-observer-task": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"queue an intersection observer task","type":"dfn","url":"#queue-an-intersection-observer-task"},
+"#queue-an-intersectionobserverentry": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"queue an intersectionobserverentry","type":"dfn","url":"#queue-an-intersectionobserverentry"},
+"#unobserve-a-target-element": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"unobserve a target element","type":"dfn","url":"#unobserve-a-target-element"},
+"#visibility": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"intersection-observer","status":"local","text":"visibility","type":"dfn","url":"#visibility"},
+"http://www.w3.org/TR/css-masking-1/#propdef-clip-path": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"","status":"anchor-block","text":"clip-path","type":"dfn","url":"http://www.w3.org/TR/css-masking-1/#propdef-clip-path"},
+"http://www.w3.org/TR/hr-time/#domhighrestimestamp": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"","status":"anchor-block","text":"DOMHighResTimeStamp","type":"typedef","url":"http://www.w3.org/TR/hr-time/#domhighrestimestamp"},
+"http://www.w3.org/TR/hr-time/#time-origin": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"","status":"anchor-block","text":"time origin","type":"dfn","url":"http://www.w3.org/TR/hr-time/#time-origin"},
+"https://dom.spec.whatwg.org/#dictdef-mutationobserverinit": {"export":true,"for_":[],"level":"1","normative":true,"shortname":"dom","spec":"dom","status":"current","text":"MutationObserverInit","type":"dictionary","url":"https://dom.spec.whatwg.org/#dictdef-mutationobserverinit"},
+"https://dom.spec.whatwg.org/#document": {"export":true,"for_":[],"level":"1","normative":true,"shortname":"dom","spec":"dom","status":"current","text":"Document","type":"interface","url":"https://dom.spec.whatwg.org/#document"},
+"https://dom.spec.whatwg.org/#dom-mutationobserver-observe": {"export":true,"for_":["MutationObserver"],"level":"1","normative":true,"shortname":"dom","spec":"dom","status":"current","text":"observe(target)","type":"method","url":"https://dom.spec.whatwg.org/#dom-mutationobserver-observe"},
+"https://dom.spec.whatwg.org/#element": {"export":true,"for_":[],"level":"1","normative":true,"shortname":"dom","spec":"dom","status":"current","text":"Element","type":"interface","url":"https://dom.spec.whatwg.org/#element"},
+"https://dom.spec.whatwg.org/#mutationobserver": {"export":true,"for_":[],"level":"1","normative":true,"shortname":"dom","spec":"dom","status":"current","text":"MutationObserver","type":"interface","url":"https://dom.spec.whatwg.org/#mutationobserver"},
+"https://dom.spec.whatwg.org/#node": {"export":true,"for_":[],"level":"1","normative":true,"shortname":"dom","spec":"dom","status":"current","text":"Node","type":"interface","url":"https://dom.spec.whatwg.org/#node"},
+"https://drafts.csswg.org/css-box-4/#propdef-margin": {"export":true,"for_":[],"level":"4","normative":true,"shortname":"css-box","spec":"css-box-4","status":"current","text":"margin","type":"property","url":"https://drafts.csswg.org/css-box-4/#propdef-margin"},
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+"https://drafts.csswg.org/css-box/#padding-area": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"","status":"anchor-block","text":"padding area","type":"dfn","url":"https://drafts.csswg.org/css-box/#padding-area"},
+"https://drafts.csswg.org/css-box/#padding-edge": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"","status":"anchor-block","text":"padding edge","type":"dfn","url":"https://drafts.csswg.org/css-box/#padding-edge"},
+"https://drafts.csswg.org/css-display/#containing-block-chain": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"","status":"anchor-block","text":"containing block chain","type":"dfn","url":"https://drafts.csswg.org/css-display/#containing-block-chain"},
+"https://drafts.csswg.org/css-overflow-3/#ink-overflow-rectangle": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"","status":"anchor-block","text":"ink overflow rectangle","type":"dfn","url":"https://drafts.csswg.org/css-overflow-3/#ink-overflow-rectangle"},
+"https://drafts.csswg.org/css-overflow-3/#overflow-properties": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"","status":"anchor-block","text":"overflow properties","type":"dfn","url":"https://drafts.csswg.org/css-overflow-3/#overflow-properties"},
+"https://drafts.csswg.org/css-overflow-3/#scroll-container": {"export":true,"for_":[],"level":"3","normative":true,"shortname":"css-overflow","spec":"css-overflow-3","status":"current","text":"scroll container","type":"dfn","url":"https://drafts.csswg.org/css-overflow-3/#scroll-container"},
+"https://drafts.csswg.org/css-overflow-3/#scrollport": {"export":true,"for_":[],"level":"3","normative":true,"shortname":"css-overflow","spec":"css-overflow-3","status":"current","text":"scrollport","type":"dfn","url":"https://drafts.csswg.org/css-overflow-3/#scrollport"},
+"https://drafts.csswg.org/css-syntax-3/#parse-a-list-of-component-values": {"export":true,"for_":[],"level":"3","normative":true,"shortname":"css-syntax","spec":"css-syntax-3","status":"current","text":"parse a list of component values","type":"dfn","url":"https://drafts.csswg.org/css-syntax-3/#parse-a-list-of-component-values"},
+"https://drafts.csswg.org/css-transforms-1/#identity-transform-function": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"","status":"anchor-block","text":"identity transform function","type":"dfn","url":"https://drafts.csswg.org/css-transforms-1/#identity-transform-function"},
+"https://drafts.csswg.org/css-transforms-1/#post-multiplied": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"","status":"anchor-block","text":"post-multiplied","type":"dfn","url":"https://drafts.csswg.org/css-transforms-1/#post-multiplied"},
+"https://drafts.csswg.org/css-transforms-1/#serialization-of-the-computed-value": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"","status":"anchor-block","text":"serialization","type":"dfn","url":"https://drafts.csswg.org/css-transforms-1/#serialization-of-the-computed-value"},
+"https://drafts.csswg.org/css-transforms-1/#transformation-matrix": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"","status":"anchor-block","text":"transformation matrix","type":"dfn","url":"https://drafts.csswg.org/css-transforms-1/#transformation-matrix"},
+"https://drafts.csswg.org/css-values-3/#absolute-length": {"export":false,"for_":[],"level":"3","normative":true,"shortname":"css-values","spec":"css-values-3","status":"current","text":"absolute length","type":"dfn","url":"https://drafts.csswg.org/css-values-3/#absolute-length"},
+"https://drafts.csswg.org/css-values-3/#dimension": {"export":true,"for_":[],"level":"3","normative":true,"shortname":"css-values","spec":"css-values-3","status":"current","text":"dimension","type":"dfn","url":"https://drafts.csswg.org/css-values-3/#dimension"},
+"https://drafts.csswg.org/css-values-4/#percentage-value": {"export":true,"for_":[],"level":"4","normative":true,"shortname":"css-values","spec":"css-values-4","status":"current","text":"<percentage>","type":"type","url":"https://drafts.csswg.org/css-values-4/#percentage-value"},
+"https://drafts.csswg.org/css2/visuren.html#viewport": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"","status":"anchor-block","text":"viewport","type":"dfn","url":"https://drafts.csswg.org/css2/visuren.html#viewport"},
+"https://drafts.csswg.org/cssom-view-1/#element-get-the-bounding-box": {"export":true,"for_":["Element"],"level":"1","normative":true,"shortname":"cssom-view","spec":"cssom-view-1","status":"current","text":"get the bounding box","type":"dfn","url":"https://drafts.csswg.org/cssom-view-1/#element-get-the-bounding-box"},
+"https://drafts.csswg.org/cssom-view-1/#pinch-zoom": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"","status":"anchor-block","text":"pinch zoom","type":"dfn","url":"https://drafts.csswg.org/cssom-view-1/#pinch-zoom"},
+"https://drafts.fxtf.org/filter-effects/#funcdef-filter-blur": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"","status":"anchor-block","text":"blur","type":"dfn","url":"https://drafts.fxtf.org/filter-effects/#funcdef-filter-blur"},
+"https://drafts.fxtf.org/geometry-1/#dictdef-domrectinit": {"export":true,"for_":[],"level":"1","normative":true,"shortname":"geometry","spec":"geometry-1","status":"current","text":"DOMRectInit","type":"dictionary","url":"https://drafts.fxtf.org/geometry-1/#dictdef-domrectinit"},
+"https://drafts.fxtf.org/geometry-1/#domrect": {"export":true,"for_":[],"level":"1","normative":true,"shortname":"geometry","spec":"geometry-1","status":"current","text":"DOMRect","type":"interface","url":"https://drafts.fxtf.org/geometry-1/#domrect"},
+"https://drafts.fxtf.org/geometry-1/#domrectreadonly": {"export":true,"for_":[],"level":"1","normative":true,"shortname":"geometry","spec":"geometry-1","status":"current","text":"DOMRectReadOnly","type":"interface","url":"https://drafts.fxtf.org/geometry-1/#domrectreadonly"},
+"https://heycam.github.io/webidl/#dfn-simple-exception": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"","status":"anchor-block","text":"SyntaxError","type":"exception","url":"https://heycam.github.io/webidl/#dfn-simple-exception"},
+"https://heycam.github.io/webidl/#dfn-throw": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"","status":"anchor-block","text":"throw","type":"dfn","url":"https://heycam.github.io/webidl/#dfn-throw"},
+"https://heycam.github.io/webidl/#idl-double": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"","status":"anchor-block","text":"double","type":"interface","url":"https://heycam.github.io/webidl/#idl-double"},
+"https://heycam.github.io/webidl/#idl-undefined": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"","status":"anchor-block","text":"undefined","type":"interface","url":"https://heycam.github.io/webidl/#idl-undefined"},
+"https://html.spec.whatwg.org/multipage/browsers.html#browsing-context": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"","status":"anchor-block","text":"browsing context","type":"dfn","url":"https://html.spec.whatwg.org/multipage/browsers.html#browsing-context"},
+"https://html.spec.whatwg.org/multipage/browsers.html#browsing-context-container": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"","status":"anchor-block","text":"browsing context container","type":"dfn","url":"https://html.spec.whatwg.org/multipage/browsers.html#browsing-context-container"},
+"https://html.spec.whatwg.org/multipage/browsers.html#fully-active": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"","status":"anchor-block","text":"fully active","type":"dfn","url":"https://html.spec.whatwg.org/multipage/browsers.html#fully-active"},
+"https://html.spec.whatwg.org/multipage/browsers.html#list-of-the-descendant-browsing-contexts": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"","status":"anchor-block","text":"list of the descendant browsing contexts","type":"dfn","url":"https://html.spec.whatwg.org/multipage/browsers.html#list-of-the-descendant-browsing-contexts"},
+"https://html.spec.whatwg.org/multipage/browsers.html#nested-browsing-context": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"","status":"anchor-block","text":"nested browsing context","type":"dfn","url":"https://html.spec.whatwg.org/multipage/browsers.html#nested-browsing-context"},
+"https://html.spec.whatwg.org/multipage/browsers.html#same-origin-domain": {"export":true,"for_":[],"level":"1","normative":true,"shortname":"html","spec":"html","status":"current","text":"same origin-domain","type":"dfn","url":"https://html.spec.whatwg.org/multipage/browsers.html#same-origin-domain"},
+"https://html.spec.whatwg.org/multipage/browsers.html#top-level-browsing-context": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"","status":"anchor-block","text":"top-level browsing context","type":"dfn","url":"https://html.spec.whatwg.org/multipage/browsers.html#top-level-browsing-context"},
+"https://html.spec.whatwg.org/multipage/dom.html#document": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"","status":"anchor-block","text":"document","type":"dfn","url":"https://html.spec.whatwg.org/multipage/dom.html#document"},
+"https://html.spec.whatwg.org/multipage/infrastructure.html#dfn-callback-this-value": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"","status":"anchor-block","text":"callback this value","type":"dfn","url":"https://html.spec.whatwg.org/multipage/infrastructure.html#dfn-callback-this-value"},
+"https://html.spec.whatwg.org/multipage/nav-history-apis.html#dom-document-2": {"export":true,"for_":["Window"],"level":"1","normative":true,"shortname":"html","spec":"html","status":"current","text":"document","type":"attribute","url":"https://html.spec.whatwg.org/multipage/nav-history-apis.html#dom-document-2"},
+"https://html.spec.whatwg.org/multipage/origin.html#origin": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"","status":"anchor-block","text":"origin","type":"dfn","url":"https://html.spec.whatwg.org/multipage/origin.html#origin"},
+"https://html.spec.whatwg.org/multipage/webappapis.html#concept-environment-top-level-origin": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"","status":"anchor-block","text":"top-level origin","type":"dfn","url":"https://html.spec.whatwg.org/multipage/webappapis.html#concept-environment-top-level-origin"},
+"https://html.spec.whatwg.org/multipage/webappapis.html#event-loop": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"","status":"anchor-block","text":"event loop","type":"dfn","url":"https://html.spec.whatwg.org/multipage/webappapis.html#event-loop"},
+"https://html.spec.whatwg.org/multipage/webappapis.html#event-loop-processing-model": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"","status":"anchor-block","text":"html event loops processing model","type":"dfn","url":"https://html.spec.whatwg.org/multipage/webappapis.html#event-loop-processing-model"},
+"https://html.spec.whatwg.org/multipage/webappapis.html#queue-a-task": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"","status":"anchor-block","text":"queue a task","type":"dfn","url":"https://html.spec.whatwg.org/multipage/webappapis.html#queue-a-task"},
+"https://html.spec.whatwg.org/multipage/webappapis.html#relevant-settings-object": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"","status":"anchor-block","text":"relevant settings object","type":"dfn","url":"https://html.spec.whatwg.org/multipage/webappapis.html#relevant-settings-object"},
+"https://html.spec.whatwg.org/multipage/webappapis.html#report-the-exception": {"export":true,"for_":[],"level":"","normative":true,"shortname":"intersection-observer","spec":"","status":"anchor-block","text":"report the exception","type":"dfn","url":"https://html.spec.whatwg.org/multipage/webappapis.html#report-the-exception"},
+"https://html.spec.whatwg.org/multipage/webappapis.html#task-source": {"export":true,"for_":[],"level":"1","normative":true,"shortname":"html","spec":"html","status":"current","text":"task source","type":"dfn","url":"https://html.spec.whatwg.org/multipage/webappapis.html#task-source"},
+"https://webidl.spec.whatwg.org/#Exposed": {"export":true,"for_":[],"level":"1","normative":true,"shortname":"webidl","spec":"webidl","status":"current","text":"Exposed","type":"extended-attribute","url":"https://webidl.spec.whatwg.org/#Exposed"},
+"https://webidl.spec.whatwg.org/#idl-DOMString": {"export":true,"for_":[],"level":"1","normative":true,"shortname":"webidl","spec":"webidl","status":"current","text":"DOMString","type":"interface","url":"https://webidl.spec.whatwg.org/#idl-DOMString"},
+"https://webidl.spec.whatwg.org/#idl-boolean": {"export":true,"for_":[],"level":"1","normative":true,"shortname":"webidl","spec":"webidl","status":"current","text":"boolean","type":"interface","url":"https://webidl.spec.whatwg.org/#idl-boolean"},
+"https://webidl.spec.whatwg.org/#idl-frozen-array": {"export":true,"for_":[],"level":"1","normative":true,"shortname":"webidl","spec":"webidl","status":"current","text":"FrozenArray","type":"interface","url":"https://webidl.spec.whatwg.org/#idl-frozen-array"},
+"https://webidl.spec.whatwg.org/#idl-long": {"export":true,"for_":[],"level":"1","normative":true,"shortname":"webidl","spec":"webidl","status":"current","text":"long","type":"interface","url":"https://webidl.spec.whatwg.org/#idl-long"},
+"https://webidl.spec.whatwg.org/#idl-sequence": {"export":true,"for_":[],"level":"1","normative":true,"shortname":"webidl","spec":"webidl","status":"current","text":"sequence","type":"dfn","url":"https://webidl.spec.whatwg.org/#idl-sequence"},
+};
+
+function mkRefHint(link, ref) {
+    const linkText = link.textContent;
+    let dfnTextElements = '';
+    if (ref.text != linkText) {
+        dfnTextElements =
+            mk.li({},
+                mk.b({}, "Term: "),
+                mk.span({}, ref.text)
+            );
+    }
+    const forList = ref.for_;
+    let forListElements;
+    if(forList.length == 0) {
+        forListElements = [];
+    } else if(forList.length == 1) {
+        forListElements = mk.li({},
+            mk.b({}, "For: "),
+            mk.span({}, forList[0]),
+        );
+    } else {
+        forListElements = mk.li({},
+            mk.b({}, "For: "),
+            mk.ul({},
+                ...forList.map(forItem =>
+                    mk.li({},
+                        mk.span({}, forItem)
+                    ),
+                ),
+            ),
+        );
+    }
+    const url = ref.url;
+    const safeUrl = encodeURIComponent(url);
+    const hintPanel = mk.aside({
+        class: "ref-hint",
+        id: `ref-hint-for-${safeUrl}`,
+        "data-for": url,
+        "aria-labelled-by": `ref-hint-for-${safeUrl}`,
+    },
+        mk.ul({},
+            dfnTextElements,
+            mk.li({},
+                mk.b({}, "URL: "),
+                mk.a({ href: url, class: "ref" }, url),
+            ),
+            mk.li({},
+                mk.b({}, "Type: "),
+                mk.span({}, `${ref.type}`),
+            ),
+            mk.li({},
+                mk.b({}, "Spec: "),
+                mk.span({}, `${ref.spec ? ref.spec : ''}`),
+            ),
+            forListElements
+        ),
+    );
+    hintPanel.forLink = link;
+    setupRefHintEventListeners(link, hintPanel);
+    return hintPanel;
+}
+
+function hideAllRefHints() {
+    queryAll(".ref-hint").forEach(el=>hideRefHint(el));
+}
+
+function hideRefHint(refHint) {
+    const link = refHint.forLink;
+    link.setAttribute("aria-expanded", "false");
+    if(refHint.teardownEventListeners) {
+        refHint.teardownEventListeners();
+    }
+    refHint.remove();
+}
+
+function showRefHint(link) {
+    if(link.classList.contains("dfn-link")) return;
+    const url = link.getAttribute("href");
+    const ref = refsData[url];
+    if(!ref) return;
+
+    hideAllRefHints(); // Only display one at this time.
+
+    const refHint = mkRefHint(link, ref);
+    append(document.body, refHint);
+    link.setAttribute("aria-expanded", "true");
+    positionRefHint(refHint);
+}
+
+function setupRefHintEventListeners(link, refHint) {
+    if (refHint.teardownEventListeners) return;
+    // Add event handlers to hide the refHint after the user moves away
+    // from both the link and refHint, if not hovering either within one second.
+    let timeout = null;
+    const startHidingRefHint = (event) => {
+        if (timeout) {
+            clearTimeout(timeout);
+        }
+        timeout = setTimeout(() => {
+            hideRefHint(refHint);
+        }, 1000);
+    }
+    const resetHidingRefHint = (event) => {
+        if (timeout) clearTimeout(timeout);
+        timeout = null;
+    };
+    link.addEventListener("mouseleave", startHidingRefHint);
+    link.addEventListener("mouseenter", resetHidingRefHint);
+    link.addEventListener("blur", startHidingRefHint);
+    link.addEventListener("focus", resetHidingRefHint);
+    refHint.addEventListener("mouseleave", startHidingRefHint);
+    refHint.addEventListener("mouseenter", resetHidingRefHint);
+    refHint.addEventListener("blur", startHidingRefHint);
+    refHint.addEventListener("focus", resetHidingRefHint);
+
+    refHint.teardownEventListeners = () => {
+        // remove event listeners
+        resetHidingRefHint();
+        link.removeEventListener("mouseleave", startHidingRefHint);
+        link.removeEventListener("mouseenter", resetHidingRefHint);
+        link.removeEventListener("blur", startHidingRefHint);
+        link.removeEventListener("focus", resetHidingRefHint);
+        refHint.removeEventListener("mouseleave", startHidingRefHint);
+        refHint.removeEventListener("mouseenter", resetHidingRefHint);
+        refHint.removeEventListener("blur", startHidingRefHint);
+        refHint.removeEventListener("focus", resetHidingRefHint);
+    };
+}
+
+function positionRefHint(refHint) {
+    const link = refHint.forLink;
+    const linkPos = getBounds(link);
+    refHint.style.top = linkPos.bottom + "px";
+    refHint.style.left = linkPos.left + "px";
+
+    const panelPos = refHint.getBoundingClientRect();
+    const panelMargin = 8;
+    const maxRight = document.body.parentNode.clientWidth - panelMargin;
+    if (panelPos.right > maxRight) {
+        const overflowAmount = panelPos.right - maxRight;
+        const newLeft = Math.max(panelMargin, linkPos.left - overflowAmount);
+        refHint.style.left = newLeft + "px";
+    }
+}
+
+// TODO: shared util
+// Returns the root-level absolute position {left and top} of element.
+function getBounds(el, relativeTo=document.body) {
+    const relativeRect = relativeTo.getBoundingClientRect();
+    const elRect = el.getBoundingClientRect();
+    const top = elRect.top - relativeRect.top;
+    const left = elRect.left - relativeRect.left;
+    return {
+        top,
+        left,
+        bottom: top + elRect.height,
+        right: left + elRect.width,
+    }
+}
+
+function showRefHintListener(e) {
+    // If the target isn't in a link (or is a link),
+    // just ignore it.
+    let link = e.target.closest("a");
+    if(!link) return;
+
+    // If the target is in a ref-hint panel
+    // (aka a link in the already-open one),
+    // also just ignore it.
+    if(link.closest(".ref-hint")) return;
+
+    // Otherwise, show the panel for the link.
+    showRefHint(link);
+}
+
+function hideAllHintsListener(e) {
+    // If the click is inside a ref-hint panel, ignore it.
+    if(e.target.closest(".ref-hint")) return;
+    // Otherwise, close all the current panels.
+    hideAllRefHints();
+}
+
+document.addEventListener("DOMContentLoaded", () => {
+    document.body.addEventListener("mousedown", showRefHintListener);
+    document.body.addEventListener("focus", showRefHintListener);
+
+    document.body.addEventListener("click", hideAllHintsListener);
+});
+
+window.addEventListener("resize", () => {
+    // Hide any open ref hint.
+    hideAllRefHints();
+});
+}
 </script>
\ No newline at end of file