code: function(operation, childNode, extra) {
  			var data,
  				modifyChild = this.tree.options.modifyChild;
  
  			if (modifyChild) {
  				if (childNode && childNode.parent !== this) {
  					$.error(
  						"childNode " + childNode + " is not a child of " + this
  					);
  				}
  				data = {
  					node: this,
  					tree: this.tree,
  					operation: operation,
  					childNode: childNode || null,
  				};
  				if (extra) {
  					$.extend(data, extra);
  				}
  				modifyChild({ type: "modifyChild" }, data);
  			}
  		}
docs: Trigger `modifyChild` event on a parent to signal that a child was modified.
  @param {string} operation Type of change: 'add', 'remove', 'rename', 'move', 'data', ...
  @param {FancytreeNode} [childNode]
  @param {object} [extra]