result using my transformer

<?xml version="1.0"?>
<playlist>
  <traklist>
    <track>
      <name>First Track!</name>
      <author>Who is it?</author>
    </track>
    <track>
      <name>My contribution</name>
      <author>Me</author>
    </track>
  </traklist>
</playlist>

rules.yaml

---
:playlist:
- []
- - //playlist
  - //pl
- :traklist:
  - []
  - - tracklist
    - tl
  - :track:
    - - :optional
    - - track
    - :name:
      - - :copy_content
      - - name
        - n_t
      :author:
      - - :copy_content
      - - author
        - a_t

yaml loader

transformer = Transformer.new( YAML::load_file("rules.yaml") )