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bug#27525: 25.1; Line wrapping of bidi paragraphs

From: Itai Berli
Subject: bug#27525: 25.1; Line wrapping of bidi paragraphs
Date: Tue, 4 Jul 2017 12:10:17 +0300

I'd like to add that this behavior breaks the Unicode bidirectional algorithm (UBA), and hence invalidates Emacs' claim of full conformance, or indeed of weak conformance, for that matter (so-called 'implicit bidirectionality' -- see section 4.2 of the UBA specifications).

The reason is that section 3.4 'Reordering Resolved Levels' of the algorithm states (I replaced the bullet points in the original by numbers):

> * The characters are shaped into glyphs [...]
> * The accumulated widths of those glyphs (in logical order) are used to determine line breaks.

The Emacs line-wrapping algorithm does not use the logical order of the glyphs to determine line breaks, as evidence by the example given in my original post, which I shall link to again: http://imgur.com/Bckn7zP

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