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   Re: [xml-dev] Binary content and allowed characters in XML

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On Thursday 20 December 2001 04:34 am, Nicolas LEHUEN wrote:
> What defines the set of allowed characters in XML content ? Is it technical
> reasons, or readability reasons ?


> The problem is, readability is a subjective concept. There's no character
> encoding that both contains all required characters for a given language
> and that are readable on all platform. If you define readability by "I can
> read it with vi under my Unix variant", you'll have hard times trying to
> find such an encoding.
. . .
> XML answers this need, as long as labels and values are 'text', whatever it
> means for the W3C (once again, UTF-8 string is no longer text for me as
> soon as I've got French accentuated characters in my strings). But for
> binary data, I have to use tricks. I don't want to.

One article that might be interesting is the "What is text really?" article.

However, something that separates text from binary data is that text 
is ultimately defined in terms of characters. The encoding of characters, and 
the display of characters, are logically distinct from the *concept* of the 
characters used. 

At this abstract level, it is questionable whether many of the control 
characters, and NUL, are actually characters at all. As Rick pointed out, 
most of them get special treatment in Unicode.

From that abstract technical level, we can also jump down to the lowest 
level, and as Daniel noted, allowing things like NUL will cause all kinds of 
problems. Rick also correctly pointed out that the control sequences can 
cause issues with other programs.


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