code: def sanitize(html)
        doc = Nokogiri::HTML::DocumentFragment.parse(html)
        if Mako.config.sanitize_images
          doc.css('img').each do |n|
            begin
              n.name = 'a'
              n.content = n['alt'] ? "📷 #{n['alt']}" : '📷 Image'
              n['href'] = URI.parse(n['src']).absolutize!(uri)
            rescue URI::InvalidURIError
              # if there's a problem, just ignore it
              next
            end
          end
        end
        doc.css('h1,h2,h3,h4,h5,h6').each { |n| n.name = 'p'; n.set_attribute('class', 'bold') }
        doc.to_s
      end
docs: Transforms img tags into a tags (if configured) and transforms h1 tags
   into p tags with the class bold
  
   @param [String] html an html document string
   @return [String] a sanitized html document string