Dear Christoph,
Thank you for your kind reply and for the links! I’ll read the contribution guidelines and follow them. I’ll start my work in the bracketed-expr-handler on my fork (https://github.com/sauliusg/jabref), and discuss with you when some code is ready.
You have also mentioned in Cleanup and file links than file renaming functionality was recently updated. Is it already in the master branch? I guess I need not to get in conflict with that change.
Regards,
Saulius