From: Kent Karlsson (email@example.com)
Date: Tue Nov 04 2008 - 11:21:09 CST
Michael Everson wrote:
> On 4 Nov 2008, at 08:09, Kent Karlsson wrote:
> >>> I know. That is why there is a loophole, but only a loophole,
> >>> in the bidi algorithm. It covers (badly) Old Italic, which is
> >>> encoded as LTR, when overriden as RTL to (sometimes, only
> >>> sometimes, using some as yet unheard of higher-level-protocol
> >>> mechanism; I can imagine them, just haven't seen any) produce
> >>> mirrored glyphs for the Old Italic letters.
> >> "The font" is supposed to do that. We've always been told this.
> > But if the bidi algorithm says not to mirror, the font [handling
> > system] should not start to mirror. The mirroring is governed by the
> > bidi algorithm. If the font mirrors glyphs anyway, it's simply a
> > flawed font.
> You say this with a lot of conviction. I don't think you're right
See http://www.unicode.org/reports/tr9/#L4, which says:
L4. A character is depicted by a mirrored glyph if and only if
(a) the resolved directionality of that character is R, and
(b) the Bidi_Mirrored property value of that character is true.
The Bidi_Mirrored property is defined by Section 4.7, Bidi
Mirrored-Normative of [Unicode]; the property values are specified in [UCD].
This rule can be overridden in certain cases; see HL6.
Note the "if and only if". Rule HL6, which provides a crude exception,
in section 4.3 (Higher-level protocols) in the same document says:
HL6. Additional mirroring.
Characters with a resolved directionality of R that do not have the
Bidi_Mirrored property can also be depicted by a mirrored glyph in
specialized contexts. Such contexts include, but are not limited to,
historic scripts and associated punctuation, private-use characters,
and characters in mathematical expressions. (See Section 6, Mirroring.)
Note the "specialized contexts" proviso.
What is your reference?
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