+var sortOrder;
+
+if ( document.documentElement.compareDocumentPosition ) {
+ sortOrder = function( a, b ) {
+ if ( !a.compareDocumentPosition || !b.compareDocumentPosition ) {
+ if ( a == b ) {
+ hasDuplicate = true;
+ }
+ return 0;
+ }
+
+ var ret = a.compareDocumentPosition(b) & 4 ? -1 : a === b ? 0 : 1;
+ if ( ret === 0 ) {
+ hasDuplicate = true;
+ }
+ return ret;
+ };
+} else if ( "sourceIndex" in document.documentElement ) {
+ sortOrder = function( a, b ) {
+ if ( !a.sourceIndex || !b.sourceIndex ) {
+ if ( a == b ) {
+ hasDuplicate = true;
+ }
+ return 0;
+ }
+
+ var ret = a.sourceIndex - b.sourceIndex;
+ if ( ret === 0 ) {
+ hasDuplicate = true;
+ }
+ return ret;
+ };
+} else if ( document.createRange ) {
+ sortOrder = function( a, b ) {
+ if ( !a.ownerDocument || !b.ownerDocument ) {
+ if ( a == b ) {
+ hasDuplicate = true;
+ }
+ return 0;
+ }
+
+ var aRange = a.ownerDocument.createRange(), bRange = b.ownerDocument.createRange();
+ aRange.selectNode(a);
+ aRange.collapse(true);
+ bRange.selectNode(b);
+ bRange.collapse(true);
+ var ret = aRange.compareBoundaryPoints(Range.START_TO_END, bRange);
+ if ( ret === 0 ) {
+ hasDuplicate = true;
+ }
+ return ret;
+ };
+}
+