code: function touchMove(element, clientX, clientY) {
  
    element[deltaXSymbol] = clientX - element[previousXSymbol];
    element[deltaYSymbol] = clientY - element[previousYSymbol];
    element[previousXSymbol] = clientX;
    element[previousYSymbol] = clientY;
    if (Math.abs(element[deltaXSymbol]) > Math.abs(element[deltaYSymbol])) {
      // Move was mostly horizontal.
      trackTo(element, clientX);
      // Indicate that the event was handled. It'd be nicer if we didn't have
      // to do this so that, e.g., a user could be swiping left and right
      // while simultaneously scrolling up and down. (Native touch apps can do
      // that.) However, Mobile Safari wants to handle swipe events near the
      // page and interpret them as navigations. To avoid having a horiziontal
      // swipe misintepreted as a navigation, we indicate that we've handled
      // the event, and prevent default behavior.
      return true;
    } else {
      // Move was mostly vertical.
      return false; // Not handled
    }
  }
docs: /*
  Invoked when the user has moved during a touch operation.