Set the opacity of the element
@param {Number} opacity The new opacity. 0 = transparent, .5 = 50% visibile, 1 = fully visible, etc
@param {Boolean/Object} [animate] a standard Element animation config object or `true` for
the default animation (`{duration: 350, easing: 'easeIn'}`)
@return {Ext.dom.Element} this
function(opacity, animate) {
        var me = this;

        if (!me.dom) {
            return me;
        }

        if (!animate || !me.anim) {
            me.setStyle('opacity', opacity);
        }
        else {
            if (typeof animate != 'object') {
                animate = {
                    duration: 350,
                    easing: 'ease-in'
                };
            }

            me.animate(Ext.applyIf({
                to: {
                    opacity: opacity
                }
            }, animate));
        }
        return me;
    }