code: function(root) {
        // establish $ instance variable
        var $ = this.$ = this.$ || {};
        // populate $ from nodes with ID from the LOCAL tree
        if (root) {
          var n$ = root.querySelectorAll("[id]");
          for (var i=0, l=n$.length, n; (i<l) && (n=n$[i]); i++) {
            $[n.id] = n;
          };
        }
      }
docs: locate nodes with id and store references to them in this.$ hash