Re: save-match-data woes

[Richard Stallman]

    That's true for application code, but what about functions that
    implement core functionality?  The latter can be run from unusual
    places, like all kinds of hooks we have around, in which case it
    should preserve the match data, right?

Some functions have the spirit of a general-purpose facility.  People
will expect those functions to be "clean"--in various ways, so we need
to make them so.  But it is not worth making all functions be "clean"
like that, and people won't expect it.