RE: Is there any elisp functions to tell whether the cursor is in a comment block?

[Drew Adams]

> Yes, you are right. It can be done. For a package consisting 
> of several files there can be a file, say
> this-package-compatibility.el, that contains this information.
> For a single elisp file I think the compatibility info can be 
> in the file itself. So maybe your suggestion is better.
> 
> I would suggest a shorter version of the compatibility line, like
>    ;; Compatibility: Emacs=20.*,21.*,22.* XEmacs=unknown

If the info is to be used in some automatic way, perhaps a convention could be
used that corresponds to the form of `emacs-major-version' and
`emac-minor-version', or `emacs-version', perhaps with wild cards.

One library might be compatible with all minor versions for Emacs 21, and
another might be compatible with all minor versions of Emacs 21 after 21.1.2,
and a third might be compatible with only 21.3.1...

That kind of thing is not much of a problem if it is only people that read a
Compatibility field. But if tools do that, then there would need to be a
well-defined syntax to communicate the various possibilities unambiguously.

`unknown' doesn't seem useful to me. But how should absence be interpreted, in
general: as unknown or incompatible?
 
> I would also suggest adding this information to all elisp files on 
> EmacsWiki. Perhaps this can be done automatically

That doesn't sound like a good idea to me. I think you're asking for trouble,
here.

> using the dates the files where added

That's definitely a bad idea, IMO - no necessary relation.

> and assuming the files only works for the 
> then current released version of Emacs?

Bad assumption. And what is the "current released version" - moving
target/interpretation.

I would advise against trying to guess compatibility like that. Let library
authors determine and specify the compatibilities explicitly. Else assume
nothing.