code: function getBefore(editor, node) {
  	let anchor;
  	if (anchor = (node.previousSibling || node.parent.contentStartToken)) {
  		return editor.getTextInBufferRange(new Range(anchor.end, node.start));
  	} else if (anchor = (node.nextSibling || node.parent.contentEndToken)) {
  		return editor.getTextInBufferRange(new Range(node.end, anchor.start));
  	}
  
  	return '';
  }
docs: Returns a string that is used to delimit properties in current node’s rule
  @param  {TextEditor} editor
  @param  {Node}       node
  @return {String}