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Re: Pretest begins end-June

From: David Kastrup
Subject: Re: Pretest begins end-June
Date: Tue, 31 May 2011 09:50:31 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.0.50 (gnu/linux)

Eli Zaretskii <address@hidden> writes:

> The first part of display string support -- reordering portions of
> text covered by display properties -- is already done and tested on my
> local branch, I was planning on merging that this week.
> The other part -- reordering the strings themselves -- is mostly local
> to bidi.c, but also involves some changes in xdisp.c, particularly in
> cursor motion and push_it/pop_it.  It's a large job, and will probably
> take a month (i.e. 4 to 5 weekends) at least, maybe a little more.
> The uncertainty here is significant: this area of the display engine
> is notoriously under-documented and full of surprises, so it's
> possible I'll need to change the design half way through because I
> find out something I'm not aware of now.  It happened before.

To give some perspective to this: one of the early adopters of display
properties in Emacs 21 pretest had been preview-latex (an AUCTeX
plugin).  And I sent about two bug reports per week to Gerd Möllmann for
months until all weird cases had been sorted out.  IIRC, by far the
worst contender for confusing the display engine was when the text
hidden by the display string contained newlines, presumably because
display matrix accounting and optimization got befuddled by it.

Newlines.  And now we are talking about R2L.

David Kastrup

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