# File lib/rd/rd2html-ext-lib.rb, line 247
      def html_head
        ret = %|<head>\n|
          ret << html_title + "\n"
          ret << html_content_type + "\n" if html_content_type
        ret << link_to_css + "\n" if link_to_css
        ret << forward_links + "\n" if forward_links
        ret << backward_links + "\n" if backward_links
        if self.head
          ret << self.head + "\n"
        else
          ret << %Q[<!-- head-element:nil -->\n]
        end
        ret << %Q[</head>]
      end