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Subject: Re: Request for objections...
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From: David Moore <dmoore@ucsd.edu>
Date: 02 Jun 1997 13:20:53 -0700
In-Reply-To: jhod@po.iijnet.or.jp's message of 02 Jun 1997 18:28:22 +0900
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jhod@po.iijnet.or.jp (P. E. Jareth Hein) writes:

> In what way can this be changed to sync with FSF-Emacs?  As they don't
> have extents, what similar functionality must I keep in mind?  I
> haven't used a version of FSF-emacs really since 19.29...  A quick
> persual through overlay.el shows me that they have 'before-string and
> 'after-string properties, so where is the cursor drawn when at either
> end of an overlay?  And while I'm at it, what are
> 'insert-in-front-hooks and 'insert-behind-hooks?  Useful enough to try 
> and support them?  I will also be implementing 'point-enter-hook and
> 'point-leave-hook on extents, so is anyone clamoring for something
> like 'modification-hooks?


modification-hooks, insert-before-hooks and insert-after-hooks can
likely be added to insdel.c.

If you want to do point-enter-hook and similar, the comment below from
insdel.c is quite appropriate.  You may also want to look in the
archives for previous discussion about the evils of these kinds of
hooks.  Ie, although it might make sense to run those hooks because of a
user moving the point into the extent (like mouse hilight), it's
probably a very bad idea to run those hooks on general entry into an
extent since _a lot_ of functions move the point around for simple
internal reasons, and you'd pay a lot of pain.

  /* Some old coder said:

     "If there were to be hooks which were run when point entered/left an
     extent, this would be the place to put them.

     However, it's probably the case that such hooks should be implemented
     using a post-command-hook instead, to avoid running the hooks as a
     result of intermediate motion inside of save-excursions, for example."

     I definitely agree with this.  PT gets moved all over the place
     and it would be a Bad Thing for any hooks to get called, both for
     the reason above and because many callers are not prepared for
     a GC within this function. --ben
   */

