Re: Questions on ZWNBS - for line initial holam plus alef

From: Peter Kirk (
Date: Tue Aug 12 2003 - 07:57:57 EDT

  • Next message: Peter Kirk: "Re: Questions on ZWNBS - for line initial holam plus alef"

    On 12/08/2003 04:17, Jon Hanna wrote:

    >>Thanks for the clarification. I probably misunderstood Jon's intention.
    >>But is there a problem if, for example, an application sees the string
    >><space, space, combining mark> and regularises it (wrongly!) to <space,
    >>combining mark>?
    >Yes, I was not saying that it wouldn't be sensible to begin a line of text
    >with a spacing diacritic (whether precomposed or created using space or
    >NBSP). I was saying that it wouldn't be sensible to begin a line with a
    >combining diacritic, since that combining diacritic would be combining with
    >a newline character which it's difficult to think of any possible sensible
    >meaning for. Attribute normalisation would change the sequence U+000A,
    ><combining> to U+0020, <combining> which would arguably change the meaning,
    >but changing the meaning of a meaningless construct isn't a problem to my
    Thanks for the clarification. I think the combining mark would not
    combine with the new line mark but would be a defective combining
    sequence. I might wish to do this simply because, according to UTR #14
    this is the only way to get a combining mark to be treated as AL as I
    might wish. Probably not the best way to do this, but not illegal!

    So it seems to me that this attribute normalisation is a problem. It is
    a problem for the higher level protocol as thinks it has created a space
    but in fact it has created a combining sequence which it must not treat
    as a space. A legal sequence at a lower level, even if meaningful,
    should not confuse the higher level. (Indeed I don't think the higher
    level ought to be confused even by illegal sequences at the lower level,
    it should be transparent as far as possible.) So the higher level
    protocol needs to know not only not to split a space, combining mark
    sequence but also not to create one where one was not present before.
    Perhaps it needs to insert a suitable separator (ZWNJ?) to ensure that
    when the space is created it is not combined with the combining mark. So
    another example of needless complication created by the long-standing
    decision to permit space as a carrier for combining marks.

    Peter Kirk (personal) (work)

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