OT Language System Tags (Was: Re: E0000 Language Tags for Archaic Greek Alphabets)

From: UList@dfa-mail.com
Date: Mon Feb 28 2005 - 22:21:32 CST

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    Peter Constable wrote:

    > Other options are to use stylistic set
    > features or 'aalt' (to select alternate glyphs one character at a time).

    But is there any coding method to select "stylistic set" features or "aalt"
    variations from a Web page?

    Or any method planned? That would solve a great many issues, without needing
    to deal with language tag registries.

    I assume that exposing an OT feature to CSS (hopefully) or XML (?) would be a
    matter for Microsoft to determine (possibly with the W3), and would not
    involve Unicode.

    > in the case of OpenType, this would
    > happen with the application specifying a particular OT language-system
    > tag and then using the 'locl' feature under that language system to

    That sounds very interesting. Depending on how it's implemented in practice.

    Are "locl" (I am BTW assuming this means "local") features something formally
    defined in the OpenType registry of OT language-system tags? Or user-definable?

    If "locl" does have to be defined in the Registry, does it seem reasonable
    that the Registry could contain many long lists of obscure variants for
    ancient languages like this? And what would the process be for Microsoft to
    become aware of and add these obscure variants, for a variety of ancient
    script systems?

    Also is there any formal or informal cooperation between the OpenType registry
    of OT language-system tags -- including "locl" -- and the Unicode Consortium
    (which I seem to think is coming up with/involved with some kind of language
    tag list??) -- or the W3 -- or some other international standard?

    Or for compatibility in Web page coding, will other smart font technologies be
    able (legally and otherwise) to make use of the Microsoft list?

    > The choice between LTR and RTL requires certain things to be done by the
    > app and certain things to be done in the font. The app should take care
    > of selecting the line direction (whether its control mechanism is a
    > formatting setting or Unicode bidi control characters), and applying
    > bidi mirroring to mirrored character pairs (per Unicode character
    > properties). Then, for the RTL runs of text, a feature should be applied
    > to select RTL variants of glyphs for non-mirror-paired characters. In
    > OpenType, the 'rtla' feature should be used for this purpose.

    Oh -- I get it! (Maybe...)

    I can define a glyph in OT as a "mirror" of another glyph -- and when the app
    tells OT it has detected a Unicode direction-override codepoint, OT will then
    swap in the "mirror" glyph.

    So my pairs of LTR/RTL language tags would not be necessary.

    *But* I wonder if/when RTL functionality would ever be implemented by
    Microsoft for Greek script...

    You see with short lines of inscription text (what we're dealing with), you
    could actually "type it backwards", that is, type:

         ESARHP KEERG YM

    And use a "Cretan Doric RTL" language tag to select the reverse glyphs in the font.

    Thanks,
    Doug

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