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'xml' in NCNames

• From: "K. Ari Krupnikov" <ari@i...>
• To: xml-dev@l...
• Date: Tue, 01 May 2001 14:48:08 +0100

Namespaces in XML [1], section 2, describes an NCName as

NCName ::= (Letter | '_') (NCNameChar)*
NCNameChar ::= Letter | Digit | '.' | '-' | '_' | CombiningChar |
Extender

There is nothing in this to prohibit 'xml' from appearing as the first
characters of an NCName, but the Rec goes on to say (in a comment - are
these normative?) that it is "An XML Name, minus the ':'". In
comparison, the Rec explicitly disallows 'xml' in prefixes [2]

Now, XML "Names beginning with the string "xml", or any string which
would match (('X'|'x') ('M'|'m') ('L'|'l')), are reserved for
standardization in this or future versions of this specification." [3]

It would seem perfectly legitimate, if ill-advised, to have NCNAmes that
start with 'xml', since these characters were originally reserved for
namespace prefixes. After all, a name such as 'prefix:xmlelement' would
not be in violation of an XML 1.0 Name [3].

But using NCNames that start with 'xml' introduces an interesting
backwards compatibility problem. If used in the default namespace, it
would appear to a non-namespaces-aware processor to be in violation of
[3].

Is there a normative solution to this issue?

Ari.

[1] http://www.w3.org/TR/REC-xml-names/#ns-decl
[2] http://www.w3.org/TR/REC-xml-names/#xmlReserved
[3] http://www.w3.org/TR/REC-xml#NT-Name

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