# File lib/maruku/output/to_html.rb, line 763
  def to_html_footnote_reference
    id = self.footnote_id

    # save the order of used footnotes
    order = @doc.footnotes_order

    # footnote has already been used
    return [] if order.include?(id)

    return [] unless @doc.footnotes[id]

    # take next number
    order << id

    num = order.index(id) + 1

    sup = xelem('sup')
    sup['id'] = "#{get_setting(:doc_prefix)}fnref:#{num}"
    a = xelem('a')
    a << xtext(num.to_s)
    a['href'] = "\##{get_setting(:doc_prefix)}fn:#{num}"
    a['rel'] = 'footnote'
    sup << a
  end