Re: Better handling of window margins

[Eli Zaretskii <eliz@gnu.org>]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: emacs-devel@gnu.org
> Date: Fri, 04 Dec 2015 08:22:26 -0500
> 
> >> Not sure what SIZING-DESCRIPTOR should look like (it could be
> >> a function which takes a size and returns a new size).
> > I don't think such a function can be implemented by any particular
> > mode, because a mode only knows well what it needs from the margins,
> > it has no better idea about other modes' needs than the rest of Emacs.
> 
> That's the point of having SIZING-DESCRIPTOR be a function: it receives
> a description of the margin chosen by "all other users" and adjusts it
> according to its own needs.

Then that function is not specific to any particular user of the
margin, and so Emacs could just always use that code, instead of
asking the users of the margins to explicitly request that.

> > functions for it.  To say nothing of the fact that having more than
> > one function again raises a problem of in what order to apply them,
> > and what would be the results of applying conflicting functions in any
> > order.
> 
> We'd push this responsibility on the package authors.

They won't know what to do with that, I think.

> If SIZING-DESCRIPTOR just returns the sum (or the max) of the provided
> size and its own use, ordering doesn't matter, for example.
> And for the remaining cases we could rely on add-function's `depth' to
> impose a particular ordering.

IIUC what you mean by "ordering", it cannot be controlled anyway, not
without non-trivial changes in the display engine.