In developing gnu-apl-mode, I have successively added more and more
features that people seems to expect to exist in any language mode. My
problem is that I'm a newbie at Emacs with only 20+ years of experience
using it, so of course I don't know all things a lang-mode can do.

After thinking that my mode was pretty complete, I discovered things like
imenu and speedbar which I had never used, but is actually pretty cool when
support was added for it.

Is there a comprehensive documentation anywhere which details all features
that such a mode can (should) implement?

Somehow, I feel that there are more features that I should support that I
simply don't know about.

Regards,
Elias