code: function (event) {
          // Default mouse behaviour should not be disabled here.
          // For example, page may needs to be slided.
          event = normalizeEvent(this.dom, event);
  
          // Mark touch, which is useful in distinguish touch and
          // mouse event in upper applicatoin.
          event.zrByTouch = true;
  
          this._lastTouchMoment = new Date();
  
          this.handler.processGesture(this, event, 'start');
  
          // In touch device, trigger `mousemove`(`mouseover`) should
          // be triggered, and must before `mousedown` triggered.
          domHandlers.mousemove.call(this, event);
  
          domHandlers.mousedown.call(this, event);
  
          setTouchTimer(this);
      }
docs: Touch开始响应函数
  @inner
  @param {Event} event