The source code

    /**
     * @class Ext.CompositeElementLite
     */
    Ext.apply(Ext.CompositeElementLite.prototype, {
    	addElements : function(els, root){
            if(!els){
                return this;
            }
            if(typeof els == "string"){
                els = Ext.Element.selectorFunction(els, root);
            }
            var yels = this.elements;
    	    Ext.each(els, function(e) {
            	yels.push(Ext.get(e));
            });
            return this;
        },

        /**
        * Clears this composite and adds the elements returned by the passed selector.
        * @param {String/Array} els A string CSS selector, an array of elements or an element
        * @return {CompositeElement} this
        */
        fill : function(els){
            this.elements = [];
            this.add(els);
            return this;
        },

        /**
         * Returns the first Element
         * @return {Ext.Element}
         */
        first : function(){
            return this.item(0);
        },

        /**
         * Returns the last Element
         * @return {Ext.Element}
         */
        last : function(){
            return this.item(this.getCount()-1);
        },

        /**
         * Returns true if this composite contains the passed element
         * @param el {Mixed} The id of an element, or an Ext.Element, or an HtmlElement to find within the composite collection.
         * @return Boolean
         */
        contains : function(el){
            return this.indexOf(el) != -1;
        },

        /**
        * Filters this composite to only elements that match the passed selector.
        * @param {String} selector A string CSS selector
        * @return {CompositeElement} this
        */
        filter : function(selector){
            var els = [];
            this.each(function(el){
                if(el.is(selector)){
                    els[els.length] = el.dom;
                }
            });
            this.fill(els);
            return this;
        },

        /**
        * Removes the specified element(s).
        * @param {Mixed} el The id of an element, the Element itself, the index of the element in this composite
        * or an array of any of those.
        * @param {Boolean} removeDom (optional) True to also remove the element from the document
        * @return {CompositeElement} this
        */
        removeElement : function(keys, removeDom){
            var me = this,
    	        els = this.elements,
    	    	el;
    	    Ext.each(keys, function(val){
    		    if ((el = (els[val] || els[val = me.indexOf(val)]))) {
    		    	if(removeDom){
                        if(el.dom){
                            el.remove();
                        }else{
                            Ext.removeNode(el);
                        }
                    }
    		    	els.splice(val, 1);
    			}
    	    });
            return this;
        }
    });