The source code

    /**
     * @class Ext.Element
     */
    Ext.Element.addMethods({
        /**
         * Creates a {@link Ext.CompositeElement} for child nodes based on the passed CSS selector (the selector should not contain an id).
         * @param {String} selector The CSS selector
         * @param {Boolean} unique (optional) True to create a unique Ext.Element for each child (defaults to false, which creates a single shared flyweight object)
         * @return {CompositeElement/CompositeElementLite} The composite element
         */
        select : function(selector, unique){
            return Ext.Element.select(selector, unique, this.dom);
        }
    });