function addClasses(element, classNames) {
  var classes = domClasses(element);

  classNames = isArray(classNames) ? classNames : classNames.split(/\s+/g);

  classNames.forEach(function(cls) {
    classes.add(cls);
  });
}
Get bounding client rect of target element(s).

@param {ContextPadTarget} target

@returns {Rect & RectTRBL}