BidiMirrored property and ancient scripts (Was Re: Plain text custom fraction input)
richard.wordingham at ntlworld.com
Thu Jul 23 13:42:50 CDT 2015
On Thu, 23 Jul 2015 12:00:06 +0200
Frédéric Grosshans <frederic.grosshans at gmail.com> wrote:
> Le 23/07/2015 00:54, Richard Wordingham a écrit :
> > Which means that Ancient Egyptian hieroglyphs are unencoded! Their
> > default direction is right-to-left, but that's only the start of the
> > trouble. The encoded hieroglyphs aren't Bidi-mirrored, so if I
> > embed then in a right-to-left override, I should get retrograde
> > characters.
> The text of the standard say that they should be mirrored in this
> case. The version 7.0.0. has the following comment on Egyptian
> hieroglyphs : (p424, p9 of pdf) :
> “When left-to-right directionality is overridden to display
> Egyptian hieroglyphic text right to left, the glyphs should be
> mirrored from those shown in the code charts.”
The UCD may trump the core specification; I'm expecting to be advised
not to trust anything in the core specification.
> Similar comments are present for other historic script (Italic,
> Runic), but also Old North Arabian, which is encoded as RTL but
> “Glyphs may be mirrored in lines whenthey have left-to-right
> directionality”. This kind of implementation at the font level is
> perfectly possible and is indeed done sometimes (see e.g. Andrew
> West’s anglo-saxon runic fonts
> The BidiMirrored property is not adapted in this case because, it is
> for a few “characters such as parentheses” (Unicode8.0.0, §4.7
> p180=pf 23 of ch04.pdf), and it is thought for a LTR default : it can
> in no way consider the case of Old North Arabian.
There had been hope until today.
> Extending this property for whole scripts would be a lot of work, and
> should be more than a Y/N property as currently, since it should
> account for cases where the glyph are
> 1. always mirrored (Egyptian, Italic, Runic. Greek ?),
> 2. sometimes mirrored (I have examples of both cases in Latin. North
> Arabian seems to be in this case too),
> 3. never mirrored (Han),
> 4. not exactly mirrored ( like for U+2232 CLOCKWISE CONTOUR INTEGRAL
> and U+221B CUBE ROOT )
> 5. And also when the behaviour under direction change is undefined (I
> have difficulties to guess what it means to have LTR Arabic or
> Syriac, or RTL Devanagari. Maybe there are some traditions for
> some complex scripts, but it makes no sense to invent a uniform
> behaviour for them)
> Currently a BidiMirrorred=N can mean anything of the above, and
> BidiMirrored=Y means (1. or 4.).
To be precise, having reread the Bidi algorithm, in particular L4 and
1) If resolved directionality is R and Bidi_Mirrored=Yes,
mirroring is mandatory.
2) If resolved directionality is L and bidirectional type is not R
or AL, mirroring is prohibited.
3) Otherwise, mirroring is optional.
It's odd that a font that reverses all the Hebrew letters is compliant
with the Unicode standard.
So, I was wrong. Not marking hieroglyphs as Bidi_Mirrored didn't stop
them being used for Ancient Egyptian in marked up text.
> By the way, I think a comment should be added in the §4.7 of the
> standard to clarify that the BidiMirrored property is not intended
> for cases like hieroglyphs or italic.
That is a stupid and dangerous remark.
If the hieroglyphs had had the BidiMirrored property corrected to Yes,
one could have had, in plain text, once fonts had caught up:
<U+132B9 EGYPTIAN HIEROGLYPH R008> for nṯr in normal left-to-right text
<U+202B RIGHT-TO-LEFT EMBEDDING, U+132B9, U+202C POP DIRECTIONAL
FORMATTING> for nṯr in retrograde left-to-right text
and embed whole paragraphs in <U+202B>...<U+202C> for right-to-left
Once your remark has been adopted in the Unicode Standard, the only
way to get consistently oriented Ancient Egyptian in plain text is to:
a) Add a complete set of right-to-left hieroglyphs.
b) Add the retrograde hieroglyphs to each set.
One hopes that Egyptian Hieroglyphs is the only script for which
mirroring or not has meaning.
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