In the case of proprietary developments of pane layouts, controls and nodes, it would be useful if we could define our own CSS styles.

I see some public and protected impl_-Methods to define com.* classes (e.g. Key) to publish CSS keys.

Please move it to the public API. Without a public API (for CSS'ing custom nodes), larger projects can hardly be separated according to developers and designers.

best regards,
  Aljoscha