Re: Fastest but still reliable way to check if in a comment

> and see if the result is non-nil.  The computation is not cheap, which
> is an issue if we are using this function in a loop.

Depends on the loop.  If the loop moves monotonically forward across
a region, then an option is to use `syntax-ppss` for the beginning of
the region and then `parse-partial-sexp` to update the previous PPSS to
the new position.

>   (memq (get-text-property (point) 'face)
>                             '(font-lock-comment-delimiter-face
>                               font-lock-comment-face))

That can work well as well, tho it depends on what failure modes you
care (or not) about, e.g.:

- Fails if jit-lock hasn't gotten to it yet (e.g. it's outside the
  displayed area).
- Fails if `face` contains a list of faces.
- Works even on comments recognized via `font-lock-keywords` rather than
  via syntax tables.
- ...


=== Stefan