code: function(handle) {
          if (!isValidID(handle)) return null;
  
          var i, j, instance;
          for (i = 0, j = instances.length; i < j; i++) {
            instance = instances[i];
            if (instance.$$mdHandle === handle) {
              return instance;
            }
          }
          return null;
        }
docs: Get a registered instance.
  @param handle the String handle to look up for a registered instance.