Emacs' implementation of the bidirectional algorithm

[Eli Zaretskii via Unicode]

> Date: Sat, 1 Jul 2017 16:36:52 +0300
> From: Itai Berli via Unicode <unicode at unicode.org>
> 
> Emacs claims to fully conform to the Unicode Bidirectional Algorithm
> 8.0.0 (see sections 22.19 'Bidirectional Editing' and 37.26
> 'Bidirectional Display' of the Emacs manual)

This is somewhat inaccurate.  For the record, the actual text of
section 22.19 if the Emacs User manual is:

  Emacs implements the Unicode Bidirectional Algorithm described in the
  Unicode Standard Annex #9, for reordering of bidirectional text for
  display.

The actual text of section 37.26 of the Emacs Lisp Reference manual
is:

  In performing this “bidirectional reordering”, Emacs follows the
  Unicode Bidirectional Algorithm (a.k.a. UBA), which is described in
  Annex #9 of the Unicode standard (<http://www.unicode.org/reports/tr9/>).
  Emacs provides a “Full Bidirectionality” class implementation of the
  UBA, consistent with the requirements of the Unicode Standard v8.0.

The "Full Bidirectionality class" part refers to section 4.2 of UAX#9,
and specifically to the fact that all of the explicit directional
formatting characters are supported, including the isolates.