Re: What is the principle?

From: Peter Kirk (
Date: Wed Mar 31 2004 - 19:15:21 EST

  • Next message: Peter Kirk: "Re: What is the principle?"

    On 31/03/2004 14:27, Mark Davis wrote:

    >While I disagree with most of what you've said on this list, it is not an
    >unreasonable proposal to change the default properties for some ranges of the
    >private use blocks. I don't think that this would, in practice, really disturb
    >any applications, because of #1 below.
    >I have, however, a few observations.
    >1. PUA properties, as is clear from Ken's excellent descriptions, are simply
    >defaults. With the exception of normalization, no Unicode implementation is
    >required to observe them. So even if this change is made, any conformant
    >implementation is free to simply ignore it and just assign its own properties.
    >This would not be a magic wand.

    Understood. But I was rather thinking that at least some implementations
    base their character properties directly on the Unicode character
    database. Isn't this what ICU does? And so, if the PUA default
    properties are the ones in the UCD, they would automatically be used by

    >2. Unicode properties are not sufficient for rendering. With technologies such
    >as Apples, all of the other work can be done in a font. With OpenType, most but
    >not all can -- in particular, reordering has to be done by the application/OS.
    >So complex scripts that require reordering still would not be interchangeable
    >without private agreement.

    This is why the suggestions made for storing character properties in the
    font are unrealistic; they require major restructuring of system
    software (close to rewriting the whole OS, as I wrote earlier), not just
    tinkering. I accept that there may be some practical limitations on PUA
    complex scripts, but I would like them to be a lot less than they are now.

    >3. Even excluding the normalization properties and other obvious inapplicable
    >properties (such as name or age), there are some 50-odd possible character
    >properties, many of them with multiple possible values: see
    >A concrete proposal would have to specify exactly which properties were
    >relevant, and what the values are for the proposed ranges. (Clearly an even
    >partition according to all the possible combinations would be completely
    >impractical.) If the goal is rendering, this means looking at the possible
    >combinations of properties that are relevant for rendering and proposing a
    >division that makes sense.

    That is why I (rather than Ernest) have discussed only rendering related
    properties like bidi and default ignorable. I realise that there may be
    other properties which need to be considered, but I am not yet sure
    which these are.

    I sense that you prefer to change the default properties of existing PUA
    characters rather than add new ones. Might it be sensible to adjust the
    properties in one of the PUA planes but leave the other one untouched?
    Has ANYONE actually defined characters in one or other of these planes,
    and if so, which? It would make more sense to change the default
    properties of a plane which no one is actually using.

    >► शिष्यादिच्छेत्पराजयम् ◄

    Peter Kirk (personal) (work)

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