# File lib/maruku/output/to_html.rb, line 844
        def to_html_footnote_reference
                id = self.footnote_id
                
                # save the order of used footnotes
                order = @doc.footnotes_order
                
                if order.include? id
                  # footnote has already been used
                  return []
          end
          
          if not @doc.footnotes[id]
            return []
    end
          
                # take next number
                order << id
                
                #num = order.size; 
                num = order.index(id) + 1
                  
                sup = Element.new 'sup'
                sup.attributes['id'] = "#{get_setting(:doc_prefix)}fnref:#{num}"
                        a = Element.new 'a'
                        a << Text.new(num.to_s)
                        a.attributes['href'] = "\##{get_setting(:doc_prefix)}fn:#{num}"
                        a.attributes['rel'] = 'footnote'
                sup << a
                        
                sup
        end