diff --git a/src/core/support.js b/src/core/support.js
index 4ef1dacab..68d20e353 100644
--- a/src/core/support.js
+++ b/src/core/support.js
@@ -3,6 +3,11 @@ define([
 	"../var/support"
 ], function( document, 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() {
 	var body = document.implementation.createHTMLDocument( "" ).body;
 	body.innerHTML = "<form></form><form></form>";