Re: [xml-dev] Why cant xml:id be numeric only ?

[John Cowan <cowan@mercury.ccil.org>]

Michael Kay scripsit:

> I seem to recall asking this once, and being told that the history
> lay in the SGML rules for abbreviated syntax. Something like allowing
> <e id="xyz"/> to be abbreviated as <e xyz>. Not that this in itself
> would make a numeric identifier ambiguous, but it would account for
> requiring an ID value to have the same syntax as an attribute name.

For the same reason, it's invalid SGML to have a DTD like this:

<!ELEMENT foo EMPTY>
<!ATTLIST foo att1 (val1|val2)
          foo att2 (val2|val3)>

because <foo val2> would be ambiguous as a short form of either <foo
att1="val2"> or <foo att2="val2">.  This restriction appears in the
final paragraph of Section 3.3.1 of the XML Recommendation:

    For interoperability, the same Nmtoken SHOULD NOT occur more than
    once in the enumerated attribute types of a single element type.

-- 
John Cowan    http://ccil.org/~cowan    cowan@ccil.org
[T]here is a Darwinian explanation for the refusal to accept Darwin.
Given the very pessimistic conclusions about moral purpose to which his
theory drives us, and given the importance of a sense of moral purpose
in helping us cope with life, a refusal to believe Darwin's theory may
have important survival value. --Ian Johnston