Scripts without Fixed Directionality (was:The Phaistos Disc)

From: Richard Wordingham (richard.wordingham@ntlworld.com)
Date: Sat Apr 08 2006 - 10:29:20 CST

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    Kenneth Whistler wrote:

    ‚Äč>> >> Well, the implementations is (as far as I can tell), not quite
    >> >> automatic...
    >> >
    >> > Correct.
    >>
    >> So where is the non-automatic part? I haven't noticed any mirroring
    >> features in OpenType lay-out.
    >
    > Despite many people's attempts to force things otherwise,
    > the Unicode Standard is not a glyph, rendering, or text layout
    > standard -- it is a character encoding standard.

    It's a character 'sequence' encoding standard, which causes a lot of
    complications with the not so sequential aspects (Indic, bidi, combining
    class).

    >> >> Also, when Greek (for instance) is written in the ancient
    >> >> boustrophedon way, <snip>
    >> >> Yet Greek letters are not given the bidi-mirrored property.

    >> > Correct. And likewise there is no need to give Phaistos Disc
    >> > symbols Bidi_Mirrored=Y.

    >> But the situations are not the same. Modern Greek has inherent
    >> directionality - is it used in modern Arabic mathematics?

    > How is that of relevance to the boustrophedon issue for ancient Greek?

    Case 1: Greek has directionality ON and bidi-mirroring.

    Isolated Greek characters in Arabic text would then be reversed, which is
    undesirable. One would not want to have to explictly specify left-to-right
    embedding for mathematical symbols. Left-to-right mark and right-to-left
    mark can then be used to select the direction of individual lines.

    This is not a good idea.

    Case 2: Greek has strong left-to-right directionality and bidi-mirroring.

    Greek characters in Arabic text then work unless they are embedded using
    right-to-left override. That would be a bad idea anyway, as all digit
    sequences would be reversed. Pairs of right-to-left override and pop
    directional formatting would have to be used used to select the direction.

    So what is the objection to bidi-mirroring but strong left-to-right
    directionality for Greek? Difficulties with accents? Or does directional
    override have more important uses for Greek?

    > And if you don't like the Greek example, then refer to Old Italic
    > or to several others of the ancient Mediterranean scripts -- which
    > also demonstrate this glyph reversal to face the direction of
    > writing.

    Why is Old Italic specified as left-to-right rather than 'other neutral'?

    >> Would it be better to encode two sets - left-to-right and right-to-left?
    >
    > No. One set, whether we are talking about letters or symbols. The
    > fact that for a long time, across a wide area, writing systems
    > flipped letters and symbols around a horizontal axis to match
    > the direction of the writing is not relevant to identity of the
    > characters per se.

    I agree about the identity. I was wondering if an objection was that
    mirrored glyphs were needed for most applications. Then one set (probably
    the left-facing set) could be in the SMP with directionality 'other neutral'
    and bibi-mirroring and the other could be shunted off to the deprecated
    plane.

    >> You would also have to
    >> do your own line-breaking.
    >
    > You have to "do your own line-breaking" in any case. In *all* cases,
    > in fact.

    Now there's a possible difference between us. It seems that when you send
    plain text e-mail, you send lines. I send paragraphs. (Not perfectly; for
    clarity, alternate paragraphs are generally blank.) Thus I expect something
    to do line-breaking to fit the display medium, as is usually done with HTML.
    While that generally works well, that would not work with boustrophedon.
    Line breaks currently have to be an inherent part of boustrophedon text,
    whereas they need not be inherent in text composed of elements of fixed
    directionality. Line breaks - or something very similar - are an inherent
    part of verse.

    > So I think the correct statement is that text editing and page
    > layout application support for boustrophedon is poor.

    > Which is hardly surprising, because it isn't used in any modern writing
    > gnitirw rof rehtie ,hcaorppa cimonogre na yllaer t'nsi ti -- metsys
    > or particularly for reading in modern contexts. Boustrophedon
    > yllaitnesse era hcihw smelborp gnitirw tneicna niatrec devlos
    > not relevant to modern uses of writing.

    Don't newspaper-style columns solve a similar problem by reducing the
    distance for the eye to flick back?

    Richard.



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