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

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

At 09:15 AM 9/22/98 -0500, Deke Smith wrote:
>Gavin Thomas Nicol, gtn@eps.inso.com said on 9/21/98 2:42 PM:
>
>>The two required encodings are UTF-16 and UTF-8. You can use any other
>>encoding you like, so long as the system you are working with supports
>>it.
>>
>>Remember: byte != character code != character != glyph
>
>It may be slightly off topic, but do you mind expanding on that last 
>line? I would be interested.
>

Glyphs represent the various shapes that a character may have when
rendered or displayed; a single character may have multiple glyphs,
and it's possible for a single glyph to represent several different
characters.  Arabic, as an example, has many different glyphs for
representing a single character.  So glyphs are not the same as
characters.

Unicode defines characters as "the smallest components of written
language that have semantic value," while character codes represent
characters as "values that reside only in a memory representation, as
strings in memory, or on disk."  Different character encoding standards will
have different character codes for the same character, and even within
Unicode, the same character code may have different encodings (UTF-7, 
UTF-8, etc.).  So, character codes are not the same as characters.

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).
  
>IANA character encoding spec I found at 
>ftp://ftp.isi.edu/in-notes/iana/assignments/character-sets do not 
>explicitly name UTF-16, but does name several flavors of Unicode(?):
>
>ISO-10646-UCS-2
>ISO-10646-UCS-4
>ISO-10646-UTF-1
>ISO-10646-Unicode-Latin1
>ISO-10646-J-1
>UNICODE-1-1
>UNICODE-1-1-UTF-7
>UTF-7
>UTF-8
>
>Which is an alias for UTF-16?
>

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).



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