add orderOfNodes function to tree library

www/common/treesome.js

@@ -146,7 +146,7 @@ define([], function () {
             if (root && el.parentNode === root.childNodes[0]) { return null; }
             return rightmostNode(previousNode(el.parentNode));
         } else {
-            return rightmostNode(el.parentNode.childNodes[i-1])
+            return rightmostNode(el.parentNode.childNodes[i-1]);
         }
     };
 
@@ -162,5 +162,22 @@ define([], function () {
         }
     };
 
+    var orderOfNodes = tree.orderOfNodes = function (a, b, root) {
+        // b might not be supplied
+        if (!b) { return; }
+        // a and b might be the same element
+        if (a === b) { return 0; }
+
+        var cur = b;
+        while (cur) {
+            cur = previousNode(cur, root);
+            // if you find 'a' while traversing backwards
+            // they are in the expected order
+            if (cur === a) { return 1; }
+        }
+        // otherwise 
+        return -1;
+    };
+
     return tree;
 });