Re: [xml-dev] Doesn't the list of allowable characters shown in the XML specification assume a Unicode character encoding scheme? What if the XML isn't using Unicode?

At 2021-04-15 12:51 +0000, Roger L Costello wrote:
>The XML specification says that these are the codepoints for the 
>characters that are allowed in XML documents:

Not quite.

>Char       ::=          #x9 | #xA | #xD | [#x20-#xD7FF] | 
>[#xE000-#xFFFD] | [#x10000-#x10FFFF]
>
>But, but, but, ....
>
>Doesn't that list of codepoints assume the XML documents are encoded 
>using a Unicode character encoding scheme?

The specification says that a "parsed entity contains text, a 
sequence of characters", and "a character is an atomic unit of text 
as specified by ISO/IEC 10646. Legal characters are tab, character 
return, line feed, and legal characters of Unicode and ISO/IEC 10646".

https://www.w3.org/TR/xml/#charsets

Separately, 4.3.3 states "In the document entity, the encoding 
declaration is part of the XML declaration".

https://www.w3.org/TR/xml/#charencoding

>What if the XML documents aren't encoded using a Unicode character 
>encoding scheme, then what are the allowable characters?

The encoding of the document entity is independent of the repertoire 
of allowable characters. If the document entity expresses a character 
that is not in the list of allowable characters, then the document is 
not well-formed.

>For example, in Unicode the codepoint #x9 corresponds to the 
>"horizontal tab" character but in EBCDIC hex 9 corresponds to the 
>"begin superscript" character. Is the XML specification saying that 
>an XML document using EBCDIC can use the invisible "begin 
>superscript" character but not the "horizontal tab" character? Or, 
>is it saying that am I expected, when using a character encoding 
>scheme other than Unicode, to convert the above list of Unicode 
>codepoints to the corresponding characters in the non-Unicode 
>character encoding scheme? For example, in EBCDIC the "horizontal 
>tab" character is 5.

Neither. The specification is saying that a document entity has an 
encoding that is independent of the definition of the text allowed in 
XML parsed entities. To get the character you want in XML (as defined 
by Unicode) use the encoding you need in your document (as defined by 
the XML Declaration).

If you try to say it using your own words, you may end up confusing 
the reader. I suggest you cite the specification.

I hope this is helpful.

. . . . . Ken


>/Roger
>
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