+var sortOrder;
+
+if ( document.documentElement.compareDocumentPosition ) {
+ sortOrder = function( a, b ) {
+ var ret = a.compareDocumentPosition(b) & 4 ? -1 : a === b ? 0 : 1;
+ if ( ret === 0 ) {
+ hasDuplicate = true;
+ }
+ return ret;
+ };
+} else if ( document.documentElement.sourceIndex === 1 ) {
+ sortOrder = function( a, b ) {
+ var ret = a.sourceIndex - b.sourceIndex;
+ if ( ret === 0 ) {
+ hasDuplicate = true;
+ }
+ return ret;
+ };
+}
+