code: function readUsedSize(element, property) {
  		var value = helpers.getStyle(element, property);
  		var matches = value && value.match(/(\d+)px/);
  		return matches? Number(matches[1]) : undefined;
  	}
docs: The "used" size is the final value of a dimension property after all calculations have
  been performed. This method uses the computed style of `element` but returns undefined
  if the computed style is not expressed in pixels. That can happen in some cases where
  `element` has a size relative to its parent and this last one is not yet displayed,
  for example because of `display: none` on a parent node.
  TODO(SB) Move this method in the upcoming core.platform class.
  @see https://developer.mozilla.org/en-US/docs/Web/CSS/used_value
  @returns {Number} Size in pixels or undefined if unknown.