bug#11381: 23.3; isearch-search-and-update issue?

[Eli Zaretskii <eliz@gnu.org>]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Date: Mon, 28 May 2012 00:23:10 -0400
> Cc: 11381@debbugs.gnu.org
> 
> > Comparing two functions can be avoided by using properties
> > on function symbols like in the patch below.
> 
> It's not perfect, but yes, it's much better.

Actually, I very much dislike this "feature" of putting properties on
function symbols, or at least the way we use it.  The problem is
documentation: there's no good place visible to users where to
document the possible values of these properties and their meanings,
so they are only documented in the code.  This makes maintenance much
harder and error-prone than it needs to be.

Look at delsel.el, for one such example.  The various uses of the
related properties, scattered through half a dozen other Lisp
packages, are completely obfuscated, and the only place you can really
understand what these properties mean is by looking at the code in
delsel.el that handles them, because even the commentary in delsel.el
leaves a lot of place for improvement.

I say, either we start documenting these properties in the doc strings
and in the manual, or we should deprecate and discourage the practice
of using them.