code: function _removeRef(refer, refee) {
          var item = _refMap[refee._id];
          if (item) {
              var count = item[refer._id];
              if (count && (count > 0)) {
                  item[refer._id] = count - 1;
              } else {
                  item[refer._id] = 0;
              }
              if (item[refer._id] === 0) {
                  delete item[refer._id];
              }
          }
      }
docs: Remove a reference from the inverted index. (Decrease refCount by one. Remove the entry if refCount reached zero)
  
  @private
  @param {Core.Element} refer Referencing element.
  @param {Core.Element} refee Referenced element.