Hebrew in markup

[Dov Grobgeld]

Thanks for the explanation, Eli.

The idea of making tags not influence the reordering of the surrounding
text nor the base direction was one of the first  use case I thought of
when I heard about the Isolation characters the first time. I believe it
would make editing BiDi HTML much easier. I'll file a feature request about
the idea.

Regards,
Dov

On Sun, Apr 5, 2015 at 11:48 AM, Eli Zaretskii <eliz at gnu.org> wrote:

> > Date: Sun, 5 Apr 2015 11:20:41 +0300
> > From: Dov Grobgeld <dov.grobgeld at gmail.com>
> > Cc: "Nadav Har'El" <nyh at math.technion.ac.il>, Dotan Cohen <
> dotancohen at gmail.com>,
> >       linux-il <linux-il at cs.huji.ac.il>
> >
> > I admit that I have very little knowledge about how font selection and
> > reordering logic works in emacs.
>
> Font selection has absolutely no bearing on this discussion.  The
> visual order is decided based on the characters' properties, not on
> how they will be drawn on the glass.  For example, they will be
> reordered even if they have no glyphs in any available font, or if you
> set up a display table to, say, display Hebrew letters as upper-case
> Latin letters.
>
> As to reordering, it happens at display time.  The mechanism that
> generates data structures used to draw font glyphs on the screen
> produces visual order from the logical order, so that those data
> structures hold the text already reordered.
>
> > One way of carrying out reordering of <h1>שלום!</h1> would be if the
> emacs
> > major mode was be able to inject the FSI...PDI characters before the
> text is
> > passed to the paragraph direction determining logic. Is this possible?
>
> No.  The logic that determines base paragraph direction is part of the
> reordering code which produces visual order from logical order.  That
> code runs as part of redisplay, and examines only the text that is in
> the buffer.  So the FSI..PDI embeddings must be present in buffer text
> to do what you want.
>
> If something like what you want is required without changing buffer
> text, there could be special text properties on some portions of
> buffer text, that would be interpreted by the display code.  But that
> isn't implemented, mainly because no one expressed any special
> interest in that, let alone presented a worked-out set of requirements
> for it.
>
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