class RDoc::Markup::Formatter

def convert_flow(flow)
  res = []
  flow.each do |item|
    case item
    when String then
      res << convert_string(item)
    when RDoc::Markup::AttrChanger then
      off_tags res, item
      on_tags res, item
    when RDoc::Markup::Special then
      res << convert_special(item)
    else
      raise "Unknown flow element: #{item.inspect}"
    end
  end
  res.join
end