/usr/lib/ruby/1.8/rdoc/markup/ is in libruby1.8 1.8.7.352-2ubuntu1.6.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/ruby/1.8/rdoc/markup/sample/
/usr/lib/ruby/1.8/rdoc/markup/sample/rdoc2latex.rb
/usr/lib/ruby/1.8/rdoc/markup/sample/sample.rb
/usr/lib/ruby/1.8/rdoc/markup/simple_markup/
/usr/lib/ruby/1.8/rdoc/markup/simple_markup.rb
/usr/lib/ruby/1.8/rdoc/markup/simple_markup/fragments.rb
/usr/lib/ruby/1.8/rdoc/markup/simple_markup/inline.rb
/usr/lib/ruby/1.8/rdoc/markup/simple_markup/lines.rb
/usr/lib/ruby/1.8/rdoc/markup/simple_markup/preprocess.rb
/usr/lib/ruby/1.8/rdoc/markup/simple_markup/to_flow.rb
/usr/lib/ruby/1.8/rdoc/markup/simple_markup/to_html.rb
/usr/lib/ruby/1.8/rdoc/markup/simple_markup/to_latex.rb
/usr/lib/ruby/1.8/rdoc/markup/test/
/usr/lib/ruby/1.8/rdoc/markup/test/AllTests.rb
/usr/lib/ruby/1.8/rdoc/markup/test/TestInline.rb
/usr/lib/ruby/1.8/rdoc/markup/test/TestParse.rb