diff --git a/interface-spec.html b/interface-spec.html
index 37b4bec..ff83139 100644
--- a/interface-spec.html
+++ b/interface-spec.html
@@ -356,8 +356,20 @@ <h3><dfn>Quad</dfn> interface</h3>
       <code>NamedNode</code>, <code>BlankNode</code> or <code>Variable</code>.
     </p>
     <p>
-      <dfn>equals()</dfn> returns <code>true</code> if and only if the argument is a) of the same
-      type b) has all components equal.
+      <dfn id="quad-equals">equals()</dfn> returns <code>true</code>
+      when called with parameter <code>other</code>
+      on an object <code>quad</code> if and only if
+      all of the conditions below hold:
+    </p>
+    <ul>
+      <li><code>other</code> is <em>neither</em> <code>null</code> nor <code>undefined</code>;</li>
+      <li><code>quad.subject.equals(other.subject)</code> evaluates to <code>true</code>;</li>
+      <li><code>quad.predicate.equals(other.predicate)</code> evaluates to <code>true</code>;</li>
+      <li><code>quad.object.equals(other.object)</code> evaluates to a <code>true</code>;</li>
+      <li><code>quad.graph.equals(other.graph)</code> evaluates to a <code>true</code>;</li>
+    </ul>
+    <p>
+      otherwise, it returns <code>false</code>.
     </p>
   </section>