function getClip(tweenProp/* , value */) {
    var ref = this;
    var element = ref.element;
    var currentClip = getStyleForProperty(element, tweenProp);
    var width = getStyleForProperty(element, 'width');
    var height = getStyleForProperty(element, 'height');
    return !/rect/.test(currentClip) ? [0, width, height, 0] : currentClip;
  }
Returns the current property computed style.
@param {string} tweenProp the property name
@returns {string | number[]} computed style for property