Well formed XML? XML references within tag names and attribute names

Question

I have been searching trying to confirm my reading of the XML spec. My interpretation is that pre-defined entities and numeric character references are not allowed in tag n

Answer 1

It seems to me that they are both wrong. According to the spec, only the following characters should be in a start tag:

":" | [A-Z] | "_" | [a-z] | [#xC0-#xD6] | [#xD8-#xF6] | [#xF8-#x2FF] | [#x370-#x37D] | [#x37F-#x1FFF] | [#x200C-#x200D] | [#x2070-#x218F] | [#x2C00-#x2FEF] | [#x3001-#xD7FF] | [#xF900-#xFDCF] | [#xFDF0-#xFFFD] | [#x10000-#xEFFFF] | "-" | "." | [0-9] | #xB7 | [#x0300-#x036F] | [#x203F-#x2040]

XMLSpy certainly isn't happy with it either. Nor <Oxygen/>.

And...just for good measure...here's what .NET had to say about it:

The '&' character, hexadecimal value 0x26, cannot be included in a name. Line 1, position 12.

What parsers are you using?

Answer 2

In digging around at w3.org, I found the following relevant pieces:

[41] Attribute ::= Name Eq AttValue [VC: Attribute Value Type] [WFC: No External Entity References] [WFC: No < in Attribute Values]

[WFC: No External Entity References] links to:

Well-formedness constraint: No External Entity References
Attribute values MUST NOT contain direct or indirect entity references to external entities.

Name links to:

[5] Name ::= NameStartChar (NameChar)*

[4] NameStartChar ::= ":" | [A-Z] | "_" | [a-z] | [#xC0-#xD6] | [#xD8-#xF6] | [#xF8-#x2FF] | [#x370-#x37D] | [#x37F-#x1FFF] | [#x200C-#x200D] | [#x2070-#x218F] | [#x2C00-#x2FEF] | [#x3001-#xD7FF] | [#xF900-#xFDCF] | [#xFDF0-#xFFFD] | [#x10000-#xEFFFF]

[4a] NameChar ::= NameStartChar | "-" | "." | [0-9] | #xB7 | [#x0300-#x036F] | [#x203F-#x2040]

Yes, it's as clear as mud! My interpretation of this would be that you could use hex entity references as long as they fell in the ranges specified above but that you could not use pre-defined references.

I would expect a well-formed error when the names don't conform to this.

Answer 3

This is very simple: no entities can be used within names. Both "parsers" are wrong here. XML specification quite clearly defines this -- there are no hidden default rules; if some construct is not included, it is not allowed.

Entities can only be used within regular character content and attribute values. And they can be included in some other places (comments, processing instructions, DTD subsets) but won't be expanded (i.e. are not recognized as entities).