RE: Proposal to add Bengali Khanda Ta

From: Marco Cimarosti (marco.cimarosti@essetre.it)
Date: Fri Nov 29 2002 - 09:17:01 EST

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    Andy White wrote:
    > Marco wrote
    > >
    > > I have a few questions:
    > >
    > > - What is the meaning of "satmaa" and "sadaatmaa"?
    >
    > 'satmaa' means stepmother. 'sadaatmaa' means 'good soul' / 'virtuous'

    Bingo! Well, nearly... My guess was that "satmaa" was the Bengali for
    "Wachstube". :-)

    German has two different words spelled "Wachstube" which pose similar
    problems, when set in Fraktur. In "Wach(-)stube" ("guards room"), "s" and
    "t" should form an "st" ligature, while in "Wachs(-)tube" ("wax tube"), "s"
    and "t" should remain separate because they are parts of two different
    roots. For Fraktur, the proposed solution is to encode the second case as
    "Wachs<ZWNJ>tube".

    But unluckily this cannot work for "satmaa" because of the special Indic
    behavior of ZWNJ.

    > > - Why is /tmaa/ spelled differently in the two words?
    >
    > 'satmaa' has the roots of 'sat' = good & 'Maa' = mother. As
    > 'Sat' is correctly spelt with a khandaTa under the rules of
    > samaas it becomes 'sat'maa'
    > sadaatmaa has the roots 'sat' = good & 'aatma' = soul /
    > spirit, and falls under the rules of sandhi and hence becomes
    > sadaatmaa.
    > (aatma is spelt with a tma conjunct).
    >
    > > - Does ISCII have a way to distinguish the two cases above
    > > and the other possible combinations? I mean:
    > > 1. Ta_Ma_Ligature,
    > > 2. Khanda_Ta + Ma,
    > > 3. Half_Ta + Ma,
    > > 4. Ta + Virama + Ma.
    >
    > 1. Ta_Ma_Ligature is simply 'ta virama ma'
    > 2. Khanda_Ta + Ma, is 'ta virama virama ma' (equivalent to
    > 'ta virama zwnj ma')
    > 3. Half_Ta + Ma is 'ta virama inv ma' (equivalent to 'ta
    > virama zwj ma')
    > 4. Ta + Virama + Ma should be 'ta virama virama inv ma' but
    > this is not implemented in the iLeap application I am using!

    Cases 1, 2 and 3 are fine. For case 4, personally, I agree that you need
    that Khanda Ta is unambiguously encoded.

    But does this unambiguous encoding of Khanda Ta necessarily have to be a new
    code point in the Bengali block? IMHO, it is possible to define an
    unambiguous sequence for Khanda Ta also using existing code points, and
    without violating their semantics.

    My counter-proposal is:
            
            09A4 + 034F + 09CD
            (TA + CGJ + VIRAMA)

    CGJ, "Combining Grapheme Joiner", is a (relatively new) zero-width character
    which has been introduced to cover some functions that could not be carried
    on well by ZWJ.

    My idea is that a display engine should uncoditionally transform the above
    sequence in a Khanda Ta glyph, *before* doing any other glyph
    transformation.

    This "strong" way of encoding Kanda Ta would anyway not exclude the default
    "soft" formation of Khanda Ta at the end of a word, whith the simple
    sequence:

            09A4 + 09CD
            (TA + VIRAMA)

    The reasons for proposing such a (relatively) complicated solution as
    opposed to the simpler solution of adding a new code point are:

    - To keep a certain compatibility with existing display engines. Upon
    sequence <09A4 + 034F + 09CD>, an old display engine would display something
    odd but, however, the text should stay *readable*.

    - To keep a good compatibility with existing non-visual software. All code
    which searches or compares text should already know what to do with CGJ:
    ignore it.

    - To try and keep the architecture of the Bengali block in sync with the
    other Indic blocks, because this helps implementers in re-using code.

    I have summarized my counter-proposal in the attached picture. Comments? Can
    it work? Is it possible to implement it in, e.g., OpenType fonts?

    _ Marco


    khanda.gif

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