Re: Chairless/Amphibious hamza

From: arno (
Date: Fri Dec 21 2007 - 00:29:45 CST

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    John Hudson wrote:
    > As I understand it, the positioning of the chairless hamza and of U+0654
    > is not the same. The chairless hamza, though above the joined letters,
    > is positioned near to where they join, while U+0654 entered in sequence
    > between the letters will be placed on the first letter (following the
    > basic Unicode rule that marks follow the letter to which they are applied).

    I simply place hamza above a tatweel. From a printers point of view
    there is no problem.

    >> Why not use U+0674 ARABIC LETTER HIGH HAMZA for the hamza BEFORE the
    >> second stroke of lam-alif?

    John Hudson wrote:
    > U+0674 is needed to form digraphs for Kazakh, which means that it
    > doesn't really behave like a combining mark. Indeed, depending on the
    > typeface design, it may be a spacing character.

    I'm curious to learn more about this. I thought that it is only used on
    the three vowel letters.

    > This may result in
    > breaking of lam_alif ligation if U+0674 is inserted between them; this
    > could be resolved with contextual glyph handling if necessary, but may
    > cause issues for some existing fonts.

    John Hudson wrote:
    > I am also not very happy with the idea of using different codepoints for
    > the same letter based on its positioning and behaviour relative to other
    > letters: this undermines the Unicode character glyph model, and I
    > believe positioning is a display issue.

    > The chairless hamza -- what Tom Milo calls the 'amphibious hamza'

    Let's not mix up things!
    The "amphibious hamza" does away -- at least for the Arabic language --
    with all hamzas presently encoded -- or did I get it wrong?
    The "chairless hamza" would only force us to add to
    U+0654 Arabic Hamza Above "do NOT use!"
    U+0655 Arabic Hamza Below "used only for decomposition of U+0623-U+0626"
    and to advice font designers not to allow Hamza above/below on any other
    char (like lam, space or tatweel).
    If I am not mistaken, Tom Milo says: One hamza for all!
    and Khaled (and arabeyes ?) say(s): Two hamzas are enough!

    > because sometimes it is floating and sometimes it is sitting, depending
    > on context -- is a topic I have given a lot of thought recently. It is
    > problematic because the modern use of the letter as a disjoining
    > character, based on several generations of typesetting technology, has
    > bred an expectation among modern readers, who find it normal that this
    > letter is disjoining. This sort of thing happens all too easily when the
    > dominant technology for typesetting a script introduces novel behaviours
    > for reasons of technical limitations.
    > So I'm thinking about the issue in terms of being able to satisfy
    > different user communities: those who want the traditional amphibious
    > hamza and those who expect the disjoining hamza.

    I hope you are not only thinking about these things, but studying them.
    So you must have some material about the influence of technology on
    hamza writing. My impression is that -- speaking for Arabic only -- the
    joining behaviour of the letters and vowels around the hamza determined
    its chair, not technology.

    > Returning to my point
    > above: I think this can be looked at as a display issue, in which case
    > the question becomes whether font formats and layout engines have
    > suitable mechanisms to handle the contextual behaviour. OpenType does,
    > and I believe Apple's AAT and SIL's Graphite do also. Tom Milo's ACE
    > technology certainly does, as he has already implemented this.

    I doubt it. Since there are different rules on the chair of hamza in
    different lands and times -- not to speak of non-Arabic languages --
    it's too hard a task even for Thomas Milo.

    > In an ideal world, the amphibious hamza would never have developed a
    > modern usage as a disjoining character,

    As stated before: Please show where hamza is disjoining and not
    disjoined by surrounding?

    > and Unicode would encode it
    > appropriately. As it is, Unicode has inherited a typesetting model that
    > is at odds with the script tradition in a number of ways,

    wayS -- which ones? (Maybe you could send me that material off the list.)

    > and we need to
    > figure out ways around these issues (especially since Unicode is
    > circumscribed by stability agreements that prevent change in many areas).
    > Generally speaking, when one is faced with different user communities,

    Indeed: For linguistics the present situation is most distasteful, but
    for a font designer I do not see a real problem.

    To end constructively: If you want to go for a "chairless hamza"
    you MUST restrict the allowed behaviour of existing characters.
    Decomposition between hamza above/below and the four precomposed letters
    (and high hamza and its three precomposed letters) is fairly
    straightforward, but chaired and chairless hamza would have to be
    separated or if that's too difficult, we must go for the ONE hamza.

    Dear Khaled, excuse my only answering John's letter.
    If I overlooked one of your points, please alert me.


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