Re: imenu fails in mode without comment-start-skip defined

[Richard Stallman]

    The whole point is efficiency compared with parse-partial-sexp -- see
    NEWS -- though that's not explicit in syntax.el's commentary.  I think
    it should be documented in lispref with parse-partial-sexp.  It should
    also be mentioned that it can clobber the match data through running
    syntax-begin-function.

I don't know this subject well enough to write about it.
I'm not sure what the programmer needs to know in order to
program efficiently using syntax-ppss.  It is true that I
could study the code and learn the answers, but that is inefficient
and my time is a limiting factor for many things.

Could someone who already knows these things please write about them?