xml-dev - Re: UTF-8 vs UTF-16...?

[David Brownell <david-b@pacbell.net>]

Kragen Sitaker wrote:
> 
> According to the latest Unicode book (is it version 2.0?  Or 3.0?)
> UTF-8 does not allow you to encode more than the first 17 planes of ISO
> 10646. 

The Unicode book has a bias:  it only talks about the Unicode
aspects of UTF-8.  I've always felt that to be a disservice,
since they didn't develop or standardize UTF-8 and are thus
spreading misinformation.  (They could at least _mention_ the
fact that they're presenting a Unicode subset of full UTF-8!)

Better information is thankfully freely accessible.  See:

    http://www.ietf.org/rfc/rfc2279.txt

which includes the details of the five and six byte encodings.

Note that even with a four byte subset of UTF-8, you can encode
characters that can't be expressed in Unicode.  A few of the
test cases in the OASIS/NIST test suite (these cases happen to
come from James Clark's XMLTEST package) have such characters;
and any conformant XML processor must report a fatal error when
it sees them.

- Dave

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