Fix validation for WYSIWYG editors

src/core.js

@@ -1032,7 +1032,7 @@ $.extend( $.validator, {
 		// meta-characters that should be escaped in order to be used with JQuery
 		// as a literal part of a name/id or any selector.
 		escapeCssMeta: function( string ) {
-			return string.replace( /([\\!"#$%&'()*+,./:;<=>?@\[\]^`{|}~])/g, "\\$1" );
+			return (string + "").replace( /([\\!"#$%&'()*+,./:;<=>?@\[\]^`{|}~])/g, "\\$1" );
 		},
 
 		idOrName: function( element ) {