class Kramdown::Converter::Html

def convert_footnote(el, _indent)
  repeat = ''
  name = @options[:footnote_prefix] + el.options[:name]
  if (footnote = @footnotes_by_name[name])
    number = footnote[2]
    repeat = ":#{footnote[3] += 1}"
  else
    number = @footnote_counter
    @footnote_counter += 1
    @footnotes << [name, el.value, number, 0]
    @footnotes_by_name[name] = @footnotes.last
  end
  "<sup id=\"fnref:#{name}#{repeat}\" role=\"doc-noteref\">" \
    "<a href=\"#fn:#{name}\" class=\"footnote\" rel=\"footnote\">" \
    "#{number}</a></sup>"
end