code: function(recognizer) {
          if (invokeArrayArg(recognizer, 'add', this)) {
              return this;
          }
  
          // remove existing
          var existing = this.get(recognizer.options.event);
          if (existing) {
              this.remove(existing);
          }
  
          this.recognizers.push(recognizer);
          recognizer.manager = this;
  
          this.touchAction.update();
          return recognizer;
      }
docs: add a recognizer to the manager
  existing recognizers with the same event name will be removed
  @param {Recognizer} recognizer
  @returns {Recognizer|Manager}