code: function (cls, done) {
          if (cls) {
              this.addClass (cls)
              this.animationend (this.$ (function () { this.removeClass (cls)
                                                       if (done) { done.call (this) } })) }
          return this }
docs: /*  1. Adds a class (that brings CSS animation)
  2. Waits until CSS animation done
  3. Removes that class
  4. Calls 'done'