def htmlify_except(nodes)
      nodes.reduce(to_html) do |output, node|
        output.gsub(node.to_html, node.to_xhtml)
      end
    end
def htmlify_except(nodes)
      nodes.reduce(to_html) do |output, node|
        output.gsub(node.to_html, node.to_xhtml)
      end
    end
Generate an html string for the current document, but replace the provided
 nodes with their xhtml strings.