code: function mouseEventPoint(mouseEvent, container) {
    const rect = container.getBoundingClientRect();
    return new Point(
      mouseEvent.clientX - rect.left - (container.clientLeft || 0),
      mouseEvent.clientY - rect.top - (container.clientTop || 0)
    );
  }
docs: Returns a Point representing a mouse event's position
  relative to a containing element.
  
  @param {MouseEvent} mouseEvent
  @param {Node} container
  @returns {Point}