bug#49963: 28.0.50; isearch failing in Dired after rectangle-mark-mode and query-replace

[Richard Stallman <rms@gnu.org>]

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  > This is a misunderstanding of what bothers me.  The problem is
  > discoverability: add-function is not easily discoverable, if it is
  > used on an internal function.  IOW, the documentation of C-s doesn't
  > tell you that its operation could be affected by that "hook".  By
  > contrast, if we use some other mechanism, like call a function via a
  > variable or call a hook, and if we document these in the doc string of
  > C-s, that problem will have disappeared, and finding causes of
  > problems such as this one would be easier.

For this reason, we had the rule that packages or libraries should not
define any advice.  Advice is for users to play with, or for code not
ready to release; it is not meant for released code to communicate
through.

However, that rule seems to have been deleted from all the
places it ought to be.  I can't find it in advice.el (though I may
have missed it; the file starts with 1500 lines of documentation).
And I can't find it in functions.texi either.

We need to document this rule again.  Can someone find it
in an old version of the Emacs Lisp Reference Manual?

-- 
Dr Richard Stallman (https://stallman.org)
Chief GNUisance of the GNU Project (https://gnu.org)
Founder, Free Software Foundation (https://fsf.org)
Internet Hall-of-Famer (https://internethalloffame.org)