RE: [xml-dev] MSXML DOM Special Chars Less Than 32

["Michael Rys" <mrys@microsoft.com>]

With all due respect, if you would have read the mail that prompted this
question, the proposal was to change the role of character entitization.

We are trying to solve a problem and that may mean to get rid of old
rules while being backwards-compatible as far as possible and with as
many agreement that we can get (ie. Get a rule into XML 1.1).

Best regards
Michael

> -----Original Message-----
> From: Mike Brown [mailto:mike@skew.org]
> Sent: Tuesday, March 26, 2002 20:44 PM
> To: xml-dev@lists.xml.org
> Subject: Re: [xml-dev] MSXML DOM Special Chars Less Than 32
> 
> James Clark wrote:
> > > How would you serialize a C# string that contains the sequence
> > > 0xD800,0xD800?  If you serialize it as ��, then what
> > > happens if somebody writes ��? Is that equivalent to
> > > 𐀀?
> 
> Michael Rys wrote:
> > This is basically a question of the encoding. If you use UTF-16 then
> > it's the parser's job to take �� and map it into the
> > encoding of the target environment. If you use UCS-4 as the
encoding,
> > then you probably did not generate �� in the first
place
> > but 𐀀...
> 
> With all due respect, this is nonsense.
> 
> 1. A character reference is a lexical construct for representing a
single
> Unicode character by its decimal or hexadecimal code point. It is not
a
> generic mechanism for representing any code point, and it is not a
> mechanism
> for representing characters by their code values in some encoding
form.
> 
> A character reference must only reference a code point that
corresponds to
> a
> Unicode character, and that character must be legal in XML. Character
> references have nothing to do with encoding, and I hope this
discussion is
> not
> proposing that XML change in this regard.
> 
> 2. Code points 0xD800-0xDFFF are *not* mapped to characters in Unicode
/
> ISO/IEC 10646. That's why they're excluded from XML's char production.
> There
> is no character number 0xD800, and there never will be.
> 
> 3. The only way to use character references to represent character #
> 0x10000
> is to write 𐀀 or 𐀀. "��" is not
well-formed
> XML
> (see WFC: Legal Character in sec. 4.1 of the spec).
> 
> The answer to James' first question is that if the C# "string" is
actually
> a
> sequence of 16-bit values, and there are no guarantees that these
values
> are
> going to conform to the rules of UTF-16 or some other predictable
> encoding,
> then it is wrong to blindly serialize that data with a mechanism that
> writes
> out the hex values preceded by "&#x" and followed by ";".
> 
> Just as one would do with the 0x0000-0x0008 and other control
characters,
> you
> look at it before you serialize it, and say "can I put this in XML or
> not",
> and if it's no way you can make a legal character out of it, then you
> ignore
> it, or you raise an exception, or (though I don't agree with this),
you
> use
> "?". You don't emit malformed XML.
> 
> 
> I understand that Michael Kay is proposing that the well-formedness
> constraint
> be modified such that "�" is legal but the bytewise encoded NUL is
> not,
> and perhaps the discussion above is based on "what if" that kind of
thing
> were
> allowed. I have issues with his proposal as well, but at least the
0x0-
> 0x1F
> code points do map to actual characters, whereas "�" and
"�"
> and
> (as another example)  "" do not.
> 
> FWIW, I am strongly against changing the definition of a character
> reference
> in order to make "�" allowable. Let's not proceed with
theoretical
> arguments that assume character references are more complex or
flexible
> than
> they actually are.
> 
>    - Mike
>
________________________________________________________________________
__
> __
>   mike j. brown                   |  xml/xslt: http://skew.org/xml/
>   denver/boulder, colorado, usa   |  resume:
http://skew.org/~mike/resume/
> 
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