code: function(element, className, options) {
          options = prepareAnimateOptions(options);
          options.addClass = mergeClasses(options.addclass, className);
          return $$animateQueue.push(element, 'addClass', options);
        }
docs: @ngdoc method
  @name $animate#addClass
  @kind function
  
  @description Triggers an addClass animation surrounding the addition of the provided CSS class(es). Upon
  execution, the addClass operation will only be handled after the next digest and it will not trigger an
  animation if element already contains the CSS class or if the class is removed at a later step.
  Note that class-based animations are treated differently compared to structural animations
  (like enter, move and leave) since the CSS classes may be added/removed at different points
  depending if CSS or JavaScript animations are used.
  
  @param {DOMElement} element the element which the CSS classes will be applied to
  @param {string} className the CSS class(es) that will be added (multiple classes are separated via spaces)
  @param {object=} options an optional collection of options/styles that will be applied to the element
  
  @return {Promise} the animation callback promise