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Rick Cameron wrote:
> From: Asmus Freytag [mailto:asmusf@ix.netcom.com]
> >Of course, the Unicode Standard 3.0 doesn't even mention a 32-bit
> >encoding - but that's not stopping uniphiles from storing Unicode data
> >in their wchar_t's!
>
> The only way such use is conformant is if it follows UTF-32. The latter is
> clearly specified in http://www.unicode.org/unicode/reports/tr19/ as:
>
> "The following lists the important features of this encoding form:
>
> UTF-32 is restricted in values to the range 0..10FFFF, which precisely
> matches the range of characters defined in the Unicode Standard (and other
> standards such as XML), and those representable by UTF-8 and UTF-16. "
Well, that's not quite true: D800..DFFF are not representable in UTF-16.
I was under the impression that as of Unicode 3.2 they would not be
legally representable in UTF-8 or UTF-32 either (i.e. that all mappings
between UTFs would be bijections between the sets of legal strings, which
is a good thing).
Does the official definition of "character" include non-characters?
Also, I don't think the comment about XML is correct, taking into account
the word "precisely"; XML allows the following subset of code points
(from http://www.w3.org/TR/REC-xml#charsets):
Char ::= #x9 | #xA | #xD | [#x20-#xD7FF] |
[#xE000-#xFFFD] | [#x10000-#x10FFFF]
So, I think the above statement should be:
UTF-32 is restricted in code point values to the ranges 0..D7FF and
E000..10FFFF, which precisely matches the set of code points designated
by the Unicode Standard (excluding surrogate code points), and those
representable by UTF-8 and UTF-16.
This set also matches the set of characters used in other standards
such as XML and HTML 4.01, with the exception of some control codes and
non-character codes.
Note "designated" instead of "defined" - is that the right term?
- --
David Hopwood <david.hopwood@zetnet.co.uk>
Home page & PGP public key: http://www.users.zetnet.co.uk/hopwood/
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This archive was generated by hypermail 2.1.2 : Wed Dec 19 2001 - 01:33:51 EST