The source code

    /**
     * @class Ext.CompositeElementLite
     * <p>This class encapsulates a <i>collection</i> of DOM elements, providing methods to filter
     * members, or to perform collective actions upon the whole set.</p>
     * <p>Although they are not listed, this class supports all of the methods of {@link Ext.Element} and
     * {@link Ext.Fx}. The methods from these classes will be performed on all the elements in this collection.</p>
     * Example:<pre><code>
    var els = Ext.select("#some-el div.some-class");
    // or select directly from an existing element
    var el = Ext.get('some-el');
    el.select('div.some-class');

    els.setWidth(100); // all elements become 100 width
    els.hide(true); // all elements fade out and hide
    // or
    els.setWidth(100).hide(true);
    </code>
     */
    Ext.CompositeElementLite = function(els, root){
        /**
         * <p>The Array of DOM elements which this CompositeElement encapsulates. Read-only.</p>
         * <p>This will not <i>usually</i> be accessed in developers' code, but developers wishing
         * to augment the capabilities of the CompositeElementLite class may use it when adding
         * methods to the class.</p>
         * <p>For example to add the <code>nextAll</code> method to the class to <b>add</b> all
         * following siblings of selected elements, the code would be</p><code><pre>
    Ext.override(Ext.CompositeElementLite, {
        nextAll: function() {
            var els = this.elements, i, l = els.length, n, r = [], ri = -1;

    //      Loop through all elements in this Composite, accumulating
    //      an Array of all siblings.
            for (i = 0; i < l; i++) {
                for (n = els[i].nextSibling; n; n = n.nextSibling) {
                    r[++ri] = n;
                }
            }

    //      Add all found siblings to this Composite
            return this.add(r);
        }
    });</pre></code>
         * @type Array
         * @property elements
         */
        this.elements = [];
        this.add(els, root);
        this.el = new Ext.Element.Flyweight();
    };

    Ext.CompositeElementLite.prototype = {
        isComposite: true,

        // private
        getElement : function(el){
            // Set the shared flyweight dom property to the current element
            var e = this.el;
            e.dom = el;
            e.id = el.id;
            return e;
        },

        // private
        transformElement : function(el){
            return Ext.getDom(el);
        },

        /**
         * Returns the number of elements in this Composite.
         * @return Number
         */
        getCount : function(){
            return this.elements.length;
        },
        /**
         * Adds elements to this Composite object.
         * @param {Mixed} els Either an Array of DOM elements to add, or another Composite object who's elements should be added.
         * @return {CompositeElement} This Composite object.
         */
        add : function(els, root){
            var me = this,
                elements = me.elements;
            if(!els){
                return this;
            }
            if(typeof els == "string"){
                els = Ext.Element.selectorFunction(els, root);
            }else if(els.isComposite){
                els = els.elements;
            }else if(!Ext.isIterable(els)){
                els = [els];
            }

            for(var i = 0, len = els.length; i < len; ++i){
                elements.push(me.transformElement(els[i]));
            }
            return me;
        },

        invoke : function(fn, args){
            var me = this,
                els = me.elements,
                len = els.length,
                e,
                i;

            for(i = 0; i < len; i++) {
                e = els[i];
                if(e){
                    Ext.Element.prototype[fn].apply(me.getElement(e), args);
                }
            }
            return me;
        },
        /**
         * Returns a flyweight Element of the dom element object at the specified index
         * @param {Number} index
         * @return {Ext.Element}
         */
        item : function(index){
            var me = this,
                el = me.elements[index],
                out = null;

            if(el){
                out = me.getElement(el);
            }
            return out;
        },

        // fixes scope with flyweight
        addListener : function(eventName, handler, scope, opt){
            var els = this.elements,
                len = els.length,
                i, e;

            for(i = 0; i<len; i++) {
                e = els[i];
                if(e) {
                    Ext.EventManager.on(e, eventName, handler, scope || e, opt);
                }
            }
            return this;
        },
        /**
         * <p>Calls the passed function for each element in this composite.</p>
         * @param {Function} fn The function to call. The function is passed the following parameters:<ul>
         * <li><b>el</b> : Element<div class="sub-desc">The current Element in the iteration.
         * <b>This is the flyweight (shared) Ext.Element instance, so if you require a
         * a reference to the dom node, use el.dom.</b></div></li>
         * <li><b>c</b> : Composite<div class="sub-desc">This Composite object.</div></li>
         * <li><b>idx</b> : Number<div class="sub-desc">The zero-based index in the iteration.</div></li>
         * </ul>
         * @param {Object} scope (optional) The scope (<i>this</i> reference) in which the function is executed. (defaults to the Element)
         * @return {CompositeElement} this
         */
        each : function(fn, scope){
            var me = this,
                els = me.elements,
                len = els.length,
                i, e;

            for(i = 0; i<len; i++) {
                e = els[i];
                if(e){
                    e = this.getElement(e);
                    if(fn.call(scope || e, e, me, i) === false){
                        break;
                    }
                }
            }
            return me;
        },

        /**
        * Clears this Composite and adds the elements passed.
        * @param {Mixed} els Either an array of DOM elements, or another Composite from which to fill this Composite.
        * @return {CompositeElement} this
        */
        fill : function(els){
            var me = this;
            me.elements = [];
            me.add(els);
            return me;
        },

        /**
         * Filters this composite to only elements that match the passed selector.
         * @param {String/Function} selector A string CSS selector or a comparison function.
         * The comparison function will be called with the following arguments:<ul>
         * <li><code>el</code> : Ext.Element<div class="sub-desc">The current DOM element.</div></li>
         * <li><code>index</code> : Number<div class="sub-desc">The current index within the collection.</div></li>
         * </ul>
         * @return {CompositeElement} this
         */
        filter : function(selector){
            var els = [],
                me = this,
                fn = Ext.isFunction(selector) ? selector
                    : function(el){
                        return el.is(selector);
                    };

            me.each(function(el, self, i) {
                if (fn(el, i) !== false) {
                    els[els.length] = me.transformElement(el);
                }
            });

            me.elements = els;
            return me;
        },

        /**
         * Find the index of the passed element within the composite collection.
         * @param el {Mixed} The id of an element, or an Ext.Element, or an HtmlElement to find within the composite collection.
         * @return Number The index of the passed Ext.Element in the composite collection, or -1 if not found.
         */
        indexOf : function(el){
            return this.elements.indexOf(this.transformElement(el));
        },

        /**
        * Replaces the specified element with the passed element.
        * @param {Mixed} el The id of an element, the Element itself, the index of the element in this composite
        * to replace.
        * @param {Mixed} replacement The id of an element or the Element itself.
        * @param {Boolean} domReplace (Optional) True to remove and replace the element in the document too.
        * @return {CompositeElement} this
        */
        replaceElement : function(el, replacement, domReplace){
            var index = !isNaN(el) ? el : this.indexOf(el),
                d;
            if(index > -1){
                replacement = Ext.getDom(replacement);
                if(domReplace){
                    d = this.elements[index];
                    d.parentNode.insertBefore(replacement, d);
                    Ext.removeNode(d);
                }
                this.elements.splice(index, 1, replacement);
            }
            return this;
        },

        /**
         * Removes all elements.
         */
        clear : function(){
            this.elements = [];
        }
    };

    Ext.CompositeElementLite.prototype.on = Ext.CompositeElementLite.prototype.addListener;

    /**
     * @private
     * Copies all of the functions from Ext.Element's prototype onto CompositeElementLite's prototype.
     * This is called twice - once immediately below, and once again after additional Ext.Element
     * are added in Ext JS
     */
    Ext.CompositeElementLite.importElementMethods = function() {
        var fnName,
            ElProto = Ext.Element.prototype,
            CelProto = Ext.CompositeElementLite.prototype;

        for (fnName in ElProto) {
            if (typeof ElProto[fnName] == 'function'){
                (function(fnName) {
                    CelProto[fnName] = CelProto[fnName] || function() {
                        return this.invoke(fnName, arguments);
                    };
                }).call(CelProto, fnName);

            }
        }
    };

    Ext.CompositeElementLite.importElementMethods();

    if(Ext.DomQuery){
        Ext.Element.selectorFunction = Ext.DomQuery.select;
    }

    /**
     * Selects elements based on the passed CSS selector to enable {@link Ext.Element Element} methods
     * to be applied to many related elements in one statement through the returned {@link Ext.CompositeElement CompositeElement} or
     * {@link Ext.CompositeElementLite CompositeElementLite} object.
     * @param {String/Array} selector The CSS selector or an array of elements
     * @param {HTMLElement/String} root (optional) The root element of the query or id of the root
     * @return {CompositeElementLite/CompositeElement}
     * @member Ext.Element
     * @method select
     * @static
     */
    Ext.Element.select = function(selector, root){
        var els;
        if(typeof selector == "string"){
            els = Ext.Element.selectorFunction(selector, root);
        }else if(selector.length !== undefined){
            els = selector;
        }else{
            throw "Invalid selector";
        }
        return new Ext.CompositeElementLite(els);
    };
    /**
     * Selects elements based on the passed CSS selector to enable {@link Ext.Element Element} methods
     * to be applied to many related elements in one statement through the returned {@link Ext.CompositeElement CompositeElement} or
     * {@link Ext.CompositeElementLite CompositeElementLite} object.
     * @param {String/Array} selector The CSS selector or an array of elements
     * @param {HTMLElement/String} root (optional) The root element of the query or id of the root
     * @return {CompositeElementLite/CompositeElement}
     * @member Ext
     * @method select
     */
    Ext.select = Ext.Element.select;