code: def render_opml(list)
        document = Nokogiri::XML(list.load_list)
        feeds.each do |feed_url|
          node = "<outline xmlUrl='#{feed_url}' />\n"
          document.xpath("//outline[@text='Subscriptions']").last.add_child node
        end
        formatted_no_decl = Nokogiri::XML::Node::SaveOptions::FORMAT +
                            Nokogiri::XML::Node::SaveOptions::NO_DECLARATION
        document.to_xml(encoding: 'utf-8', save_with: formatted_no_decl)
      end
docs: Append feeds to current subscription list and return XML document
  
   @return [String]