convert_flow

# File lib/rdoc/markup/simple_markup/to_flow.rb, line 148
    def convert_flow(flow)
      res = ""
      flow.each do |item|
        case item
        when String
          res << convert_string(item)
        when AttrChanger
          off_tags(res, item)
          on_tags(res,  item)
        when Special
          res << convert_special(item)
        else
          raise "Unknown flow element: #{item.inspect}"
        end
      end
      res
    end