state = []
ARGF.each do |line|
  state.push :input    if line =~ /<input>/
  state.push :ordered  if line =~ /<ordered-list>/
  state.push :bulleted if line =~ /<bulleted-list>/
  state.pop            if line =~ /<end-list>/ or
                          line =~ /<\/input>/

  if line =~ /<item>/
    case state.last
    when :ordered
      line.gsub!( /<item>/, "<ordered-item>" )
    when :bulleted
      line.gsub!( /<item>/, "<bulleted-item>" )
    else
      ## do nothing
    end
  end

  puts line
end