Re: encoding ext Latin for PNG

From: Peter Constable (peter_constable@sil.org)
Date: Fri Mar 10 2000 - 09:53:29 EST


       First of all, apologies for the attachment problem. This is the
       first time I've wanted to distribute a file to this list, and
       file size limitations never even dawned on my few grey cells.
       So, the file in question is available at

       ftp://ftp.sil.org/unicode/png_enc/png codepage.pdf

       Secondly, Kent wrote:
>SpecialCasing.txt (and UTR 21) appear to allow mapping to
>"not immediately related" characters. Maybe the ones you
>enumerate should be added to SpecialCasing.txt?

       If U-bar (e.g.) is encoded as 0055 + 0335, then of course this
       would be a special case of casing (no pun intended). The text
       of UTR-21 says

       <quote>
       Case mappings may produce strings of different length than the
       original. For
       example, the German character 00DF "" small letter sharp s
       expands when
       uppercased to the sequence of two characters "SS". This also
       occurs where
       there is no precomposed character corresponding to a case
       mapping.
       </quote>

       The last sentence is applicable here: there are no precomposed
       upper case characters corresponding to

       U+026B LATIN SMALL LETTER L WITH MIDDLE TILDE
       U+0289 LATIN SMALL LETTER U BAR
       U+019A LATIN SMALL LETTER L WITH BAR

       However, when I look in SpecialCasing.txt, all of the Latin
       characters of this sort that are handled in this file have a
       canonical or compatibility decomposition. The ones that I've
       mentioned do not. I didn't know if that mattered at all in
       relation to normalizations. This was my question #2. The
       corollary question is whether or not there is a need for LATIN
       CAPITAL LETTER U BAR, etc.

       I suppose that the greater likelihood of problems would lie in
       the instances where one case had a decomposition but the other
       case did not. I was just hoping to get some authoritative
       feedback to educate me about such matters.

       Peter



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