A while ago someone asked on the mailing list if there was a tutorial for writing syntax files but there was no adequate response. While the existing jsf files (in particular c.jsf) have a lot of comments, that's not enough for everybody to get started. That's why while writing the Go syntax file I took the time to write a tutorial about the process. I think it would make a good addition to the Joe documentation.
Tutorial for writing .jsf syntax files