dojo_app/js/library/dijit/_Contained.js

define([
	"dojo/_base/declare", // declare
	"./registry"	// registry.getEnclosingWidget(), registry.byNode()
], function(declare, registry){

	// module:
	//		dijit/_Contained

	return declare("dijit._Contained", null, {
		// summary:
		//		Mixin for widgets that are children of a container widget
		// example:
		//	|	// make a basic custom widget that knows about its parents
		//	|	declare("my.customClass",[dijit._WidgetBase, dijit._Contained],{});

		_getSibling: function(/*String*/ which){
			// summary:
			//		Returns next or previous sibling
			// which:
			//		Either "next" or "previous"
			// tags:
			//		private
			var p = this.getParent();
			return (p && p._getSiblingOfChild && p._getSiblingOfChild(this, which == "previous" ? -1 : 1)) || null;	// dijit/_WidgetBase
		},

		getPreviousSibling: function(){
			// summary:
			//		Returns null if this is the first child of the parent,
			//		otherwise returns the next element sibling to the "left".

			return this._getSibling("previous"); // dijit/_WidgetBase
		},

		getNextSibling: function(){
			// summary:
			//		Returns null if this is the last child of the parent,
			//		otherwise returns the next element sibling to the "right".

			return this._getSibling("next"); // dijit/_WidgetBase
		},

		getIndexInParent: function(){
			// summary:
			//		Returns the index of this widget within its container parent.
			//		It returns -1 if the parent does not exist, or if the parent
			//		is not a dijit/_Container

			var p = this.getParent();
			if(!p || !p.getIndexOfChild){
				return -1; // int
			}
			return p.getIndexOfChild(this); // int
		}
	});
});