Now the reason I needed to post the previous maintenance release is to make way for the new cool experimental feature. Didn't expect that I'll be able to implement it in just a day.
Behold and see the v0.42 with the Side track concept!
The editor now runs two copies of an engine with two separate tracks that are sharing the same song structure and settings. The original, now called Main, track gets edited and exported the usual way. The Side track only gets played in the editor, it is saved in the module file, but does not affect the export in any way.
The Main and Side tracks can be played separately or mixed together. The purpose of this is to add an extra room to sketch out the music parts and carefully plan their integration into songs of a very limited polyphony, such as 1-2 channel engines.
Functions are there to manage the Side track content, like exchanging and copying selections between two tracks. You can just exchange the contents (Ctrl+T), or copy notes from the Side track over the notes in the Main track (Ctrl+B), or use notes from the Side track to fill the gaps in the Main track (Shift+B).
Additionally, you can unwind notes within a selection (Ctrl+W), i.e. duplicate every continuous note into all subsequent empty fields, which may come handy later to fill the gaps via Shift+B.
Be aware that most beeper engines have a loose timing, so they'll eventually get de-synced to each other, even between copies of itself. Only a handful of beeper engines and most of sound chip targeted engines can maintain a stable sync for long periods of time.