bug#22786: 25.1.50; eww arabic rendering

[Eli Zaretskii <eliz@gnu.org>]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: mohamed.hibti@gmail.com,  22786@debbugs.gnu.org
> Date: Fri, 26 Feb 2016 16:15:38 +1030
> 
> > I think at this stage we should add to the eww menu an item that
> > allows to change the page direction, and let users override the
> > default if needed.  This should solve most, if not all, of the cases
> > where the default doesn't DTRT.
> 
> Well, Firefox displays the web page correctly without Firefox users
> having to do anything in particular, so presumably eww should be able to
> do the same, I would have thought?

EWW has a long way to go until it becomes a fair runner-up for
Firefox.  With all due respect.  E.g., our layout is nowhere as pretty
as Firefox, see how we display a typical Wikipedia page.

I think the catastrophic results of rendering the likes of "Other
languages" part of a Wikipedia page with Arabic the first language in
the list are much worse than an occasional need to switch the page
direction: the former affects _all_ Emacs users, while the latter
affects only those who frequently browse RTL pages.

> That is, eww should leave `bidi-paragraph-direction' to nil (which makes
> the Al Jazeera web page display correctly), and then it...  shouldn't be
> so eager to switch the direction of paragraphs to rtl just because a
> section starts with some rtl text.  Or something.

If you can come up with that magical "something", i.e. point out some
HTML tag or something else on the page that could be a hint for us not
to switch paragraph direction, then we can do that.  I will be happy
to help with the details.  But if there's no such hint, and all we
have is the text itself, then the UBA determines the paragraph
direction from the first strong directional character, and we then
keep that direction until the paragraph ends, which is indicated by an
empty line.  There's no way around this, it's how the bidirectional
display engine works.

Specifically, we need a way to distinguish between the list of
languages on a Wikipedia page from the Al Jazeera home page.  Can you
spot anything in the page sources that will allow such a distinction?

In any case, I think it will be good to add a "Switch page direction"
menu item to EWW on the emacs-25 branch.