class Kramdown::Parser::Kramdown

def parse_footnote_marker
  @src.pos += @src.matched_size
  fn_def = @doc.parse_infos[:footnotes][@src[1]]
  if fn_def
    valid = fn_def[:marker] && fn_def[:marker].options[:stack][0..-2].zip(fn_def[:marker].options[:stack][1..-1]).all? do |par, child|
      par.children.include?(child)
    end
    if !fn_def[:marker] || !valid
      fn_def[:marker] = Element.new(:footnote, nil, nil, :name => @src[1])
      fn_def[:marker].options[:stack] = [@stack.map {|s| s.first}, @tree, fn_def[:marker]].flatten.compact
      @tree.children << fn_def[:marker]
    else
      warning("Footnote marker '#{@src[1]}' already appeared in document, ignoring newly found marker")
      add_text(@src.matched)
    end
  else
    warning("Footnote definition for '#{@src[1]}' not found")
    add_text(@src.matched)
  end
end