code: function msPointerDown(inEvent) {
    this.pointerMap[inEvent.pointerId.toString()] = inEvent;
    const e = this.prepareEvent_(inEvent);
    this.dispatcher.down(e, inEvent);
  }
docs: Handler for `msPointerDown`.
  
  @this {MsSource}
  @param {MSPointerEvent} inEvent The in event.