diff --git a/src/WebformBuilder.js b/src/WebformBuilder.js
index 07919b68d0..615c156fec 100644
--- a/src/WebformBuilder.js
+++ b/src/WebformBuilder.js
@@ -1265,6 +1265,7 @@ export default class WebformBuilder extends Component {
   highlightInvalidComponents() {
     const repeatablePaths = this.findRepeatablePaths();
     let hasInvalidComponents = false;
+    // Matches anything expect letters and  '_' at the begginnig of the key and anything except of letters, numbers, '-', '.' and '_' in the rest of the key
     const badCharacters = /^[^A-Za-z_]+|[^A-Za-z0-9\-._]+/g;
 
     this.webform.everyComponent((comp) => {