RE: Question about the directionality of "Old Hungarian" (document N3531)

From: Kent Karlsson (kent.karlsson14@comhem.se)
Date: Tue Nov 04 2008 - 11:21:09 CST

  • Next message: John Hudson: "Re: Question about the directionality of "Old Hungarian" (document N3531)"

    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
    > though.

    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?

            /kent k

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