code: function _offset( box, doc ) {
  	const body = doc.body || doc.getElementsByTagName( 'body' )[ 0 ];
  	const docEl = doc.documentElement || body.parentNode;
  	const clientTop = docEl.clientTop || body.clientTop || 0;
  	const clientLeft = docEl.clientLeft || body.clientLeft || 0;
  	const scrollTop = window.pageYOffset || docEl.scrollTop;
  	const scrollLeft = window.pageXOffset || docEl.scrollLeft;
  
  	return {
  		top: box.top + scrollTop - clientTop,
  		left: box.left + scrollLeft - clientLeft,
  	};
  }
docs: Extracted from `timoxley/offset`, but directly using a
  TextRectangle instead of getting another version.
  
  @param {TextRectangle} box - result from a `getBoundingClientRect()` call
  @param {Document} doc - Document instance to use
  @return {Object} an object with `top` and `left` Number properties
  @api private