source: Dev/trunk/src/client/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 node = this.domNode;
                        do{
                                node = node[which+"Sibling"];
                        }while(node && node.nodeType != 1);
                        return node && registry.byNode(node);   // 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
                }
        });
});