class Nokogiri::XML::Builder

def insert(node, &block)
  node = @parent.add_child(node)
  if block
    begin
      old_parent = @parent
      @parent = node
      @arity ||= block.arity
      if @arity <= 0
        instance_eval(&block)
      else
        yield(self)
      end
    ensure
      @parent = old_parent
    end
  end
  NodeBuilder.new(node, self)
end