setElement(element, delegate) {
    if (this.$el) this.undelegateEvents()
    /**
     * the dom element wrapped by `$`
     *
     * @property $el
     * @type import("clappr-zepto").ZeptoCollection
     */
    this.$el = $.zepto.isZ(element) ? element : $(element)
    /**
     * the dom element itself
     *
     * @property el
     * @type HTMLElement
     */
    this.el = this.$el[0]
    if (delegate !== false) this.delegateEvents()
    return this
  }
set element to `el` and `$el`
@method setElement
@param {HTMLElement} element
@param {Boolean} delegate whether is delegate or not
@return {UIObject} itself