docs: function handleTouchStart(event) {
    if (event.touches.length == 1) {
      touchDX = 0;
      touchDY = 0;
  
      touchStartX = event.touches[0].pageX;
      touchStartY = event.touches[0].pageY;
  
      document.body.addEventListener('touchmove', handleTouchMove, true);
      document.body.addEventListener('touchend', handleTouchEnd, true);
    }
  }