The source code

    /**
     * @class Ext.dd.Registry
     * Provides easy access to all drag drop components that are registered on a page.  Items can be retrieved either
     * directly by DOM node id, or by passing in the drag drop event that occurred and looking up the event target.
     * @singleton
     */
    Ext.dd.Registry = function(){
        var elements = {};
        var handles = {};
        var autoIdSeed = 0;

        var getId = function(el, autogen){
            if(typeof el == "string"){
                return el;
            }
            var id = el.id;
            if(!id && autogen !== false){
                id = "extdd-" + (++autoIdSeed);
                el.id = id;
            }
            return id;
        };

        return {
        /**
         * Resgister a drag drop element
         * @param {String/HTMLElement} element The id or DOM node to register
         * @param {Object} data (optional) An custom data object that will be passed between the elements that are involved
         * in drag drop operations.  You can populate this object with any arbitrary properties that your own code
         * knows how to interpret, plus there are some specific properties known to the Registry that should be
         * populated in the data object (if applicable):
         * <pre>
    Value      Description<br />
    ---------  ------------------------------------------<br />
    handles    Array of DOM nodes that trigger dragging<br />
               for the element being registered<br />
    isHandle   True if the element passed in triggers<br />
               dragging itself, else false
    </pre>
         */
            register : function(el, data){
                data = data || {};
                if(typeof el == "string"){
                    el = document.getElementById(el);
                }
                data.ddel = el;
                elements[getId(el)] = data;
                if(data.isHandle !== false){
                    handles[data.ddel.id] = data;
                }
                if(data.handles){
                    var hs = data.handles;
                    for(var i = 0, len = hs.length; i < len; i++){
                    	handles[getId(hs[i])] = data;
                    }
                }
            },

        /**
         * Unregister a drag drop element
         * @param {String/HTMLElement} element The id or DOM node to unregister
         */
            unregister : function(el){
                var id = getId(el, false);
                var data = elements[id];
                if(data){
                    delete elements[id];
                    if(data.handles){
                        var hs = data.handles;
                        for(var i = 0, len = hs.length; i < len; i++){
                        	delete handles[getId(hs[i], false)];
                        }
                    }
                }
            },

        /**
         * Returns the handle registered for a DOM Node by id
         * @param {String/HTMLElement} id The DOM node or id to look up
         * @return {Object} handle The custom handle data
         */
            getHandle : function(id){
                if(typeof id != "string"){ // must be element?
                    id = id.id;
                }
                return handles[id];
            },

        /**
         * Returns the handle that is registered for the DOM node that is the target of the event
         * @param {Event} e The event
         * @return {Object} handle The custom handle data
         */
            getHandleFromEvent : function(e){
                var t = Ext.lib.Event.getTarget(e);
                return t ? handles[t.id] : null;
            },

        /**
         * Returns a custom data object that is registered for a DOM node by id
         * @param {String/HTMLElement} id The DOM node or id to look up
         * @return {Object} data The custom data
         */
            getTarget : function(id){
                if(typeof id != "string"){ // must be element?
                    id = id.id;
                }
                return elements[id];
            },

        /**
         * Returns a custom data object that is registered for the DOM node that is the target of the event
         * @param {Event} e The event
         * @return {Object} data The custom data
         */
            getTargetFromEvent : function(e){
                var t = Ext.lib.Event.getTarget(e);
                return t ? elements[t.id] || handles[t.id] : null;
            }
        };
    }();