diff --git a/src/core/support.js b/src/core/support.js
index eb88d8bf9..e15450275 100644
--- a/src/core/support.js
+++ b/src/core/support.js
@@ -2,6 +2,11 @@ define([
 	"../var/support"
 ], function( support ) {
 
+// Support: Safari 8+
+// In Safari 8 documents created via document.implementation.createHTMLDocument
+// collapse sibling forms: the second one becomes a child of the first one.
+// Because of that, this security measure has to be disabled in Safari 8.
+// https://bugs.webkit.org/show_bug.cgi?id=137337
 support.createHTMLDocument = (function() {
 	if ( !document.implementation.createHTMLDocument ) {
 		return false;