Extend print-only to bar numbers range

[fsarud]

First of all, thank you so much for developing lyluatex. It has become an essential tool in my daily work.
I wanted to suggest an improvement. Just as it’s possible to select certain systems from a large LilyPond file (the print-only option), it would be even better to be able to specify a range of measures for a fragment. LilyPond allows you to specify one or more fragments based on measure numbers using the clip-regions variable within a \layout block and the -dclip-systems option, so I suspect this wouldn’t be too far beyond lyluatex’s capabilities. My knowledge of Lua is quite limited, but I’d be happy to start looking into the possibility of implementing something like this if it’s feasible.
Best regards!

[MacLotsen]

LilyPond itself supports this through clip-regions inside a \layout block, used together with -dclip-systems.

For lyluatex I would not want to invent a separate option such as measure-range, because that would create a second syntax next to LilyPond’s own mechanism. If implemented, the public-facing option should probably stay as close as possible to LilyPond’s clip-regions.

The open question is how lyluatex should expose that. One possible approach would be to accept a lyluatex option named clip-regions and pass its value through unchanged into the generated LilyPond layout block, while also adding -dclip-systems to the LilyPond command. That option syntax is not something LilyPond itself defines; it would be the lyluatex key-value wrapper around LilyPond’s existing variable.

The main implementation work would then be:

1. register a clip-regions option in lyluatex,
2. inject it into the LilyPond \layout block,
3. run LilyPond with -dclip-systems,
4. detect and include the generated clipped output files.