# File lib/nokogiri/xml/node.rb, line 252
      def add_previous_sibling(node)
        Node.verify_nodeishness(node)
        if node.type == DOCUMENT_FRAG_NODE
          node.children.each do |child|
            add_previous_sibling_node child
          end
        else
          add_previous_sibling_node node
        end
      end