code: function _handleSingleMutation(mutation) {
    var addedNodes = _toArray(mutation.addedNodes);
    var addedRefs = addedNodes.filter(_isRefNode);
  
    // assign added nodes
    addedRefs.map(_assignRef.bind(this));
  
    var removedNodes = _toArray(mutation.removedNodes);
    var removedRefs = removedNodes.filter(_isRefNode);
  
    // assign removed nodes
    removedRefs.map(_deleteRef.bind(this));
  }
docs: Callback to detect added and removed nodes from a single mutation
  @method _handleSingleMutation
  @param {MutationRecord} mutation
  @returns {undefined}