xml-dev - RE: Mix encodings in a document?

[Jerome McDonough <jmcdonou@library.berkeley.edu>]

At 01:23 PM 9/22/98 -0400, Gavin Thomas Nicol wrote:
>> And Unicode represents a character as a single 16 bit word, so bytes
>> do not represent characters (even in UTF-8, where a character encoding
>> may be one to four bytes).
>
>This is no longer true. 

I'll accept that (I haven't seen Unicode 2.1 yet), but which part is no
longer true?

>> ISO-10646-UCS-2 (the 2-octet Basic Multilingual Plane) is the
>> same as Unicode (which is a 16-bit chararacter encoding), so
>> that would be your "UTF-16." (I don't think that, technically,
>> the 16-bit encoding gets referred to as a UCS Transmission Format).
>
>This is not correct. UTF-16 has not (to the best of my knowledge)
>been registered yet. UTF-16 differs from UCS-2 in some ways, the most
>significant of which is that it allows surrogate pairs (two 16 bit
>codes that represent a single logical character code).
>

OK, I shouldn't answer e-mail before coffee.  But let me check
this with you to see if I've got the spec. right (and make sure
they didn't change this in 2.1 as well).  Under Unicode version 2.0,
what I should've said is:

	Unicode == ISO-10646-UCS-2 != UTF-16

as Unicode and 10646 in UCS-2 format should be identical, but UTF-16
differs from both of these in it allows the use of code surrogate
pairs to enable encoding the BMP and next 16 planes of UCS-4.  From
what I can see at Unicode's home page, it now looks like Unicode is
dropping UCS-2 character encoding and now only endorses UTF-8 and 
UTF-16, so that the situation now is:

	Unicode != ISO-10646-UCS-2

and Unicode sometimes does/sometimes does not equal UTF-16.  Is that
more or less the case at the moment?


Jerome McDonough -- jmcdonou@library.Berkeley.EDU  |  (......)
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