diff --git a/src/event.js b/src/event.js
index 87ae3a65b..a5b8d597d 100644
--- a/src/event.js
+++ b/src/event.js
@@ -24,6 +24,8 @@ function returnFalse() {
 	return false;
 }
 
+// Support: IE9
+// See #13393 for more info
 function safeActiveElement() {
 	try {
 		return document.activeElement;
@@ -439,7 +441,10 @@ jQuery.event = {
 			delegateCount = handlers.delegateCount,
 			cur = event.target;
 
+		// Support (at least): Chrome, IE9
 		// Find delegate handlers
+		//
+		// Support: Firefox
 		// Black-hole SVG <use> instance trees (#13180)
 		// Avoid non-left-click bubbling in Firefox (#3861)
 		if ( delegateCount && cur.nodeType && (!event.button || event.type !== "click") ) {
@@ -669,6 +674,8 @@ jQuery.event = {
 
 jQuery.removeEvent = document.removeEventListener ?
 	function( elem, type, handle ) {
+
+		// This "if" is needed for plain objects
 		if ( elem.removeEventListener ) {
 			elem.removeEventListener( type, handle, false );
 		}