code: public Node before(Node node) {
          Validate.notNull(node);
          Validate.notNull(parentNode);
  
          parentNode.addChildren(siblingIndex, node);
          return this;
      }
docs: Insert the specified node into the DOM before this node (i.e. as a preceding sibling).
  @param node to add before this node
  @return this node, for chaining
  @see #after(Node)