[relax-ng-comment] Restriction of ID(REF(S)) compatibility feature tosingleton element name classes

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

The RELAX NG DTD Compatibility spec says that in DTD compatibility mode,
the element ancestor of an attribute of type ID(REF(S)) must have a
singleton name, disallowing patterns like this:

element foo | bar | baz {
	attribute id {xsd:ID},
	text
	}

But I don't understand why, and the issues list is not helpful.  This
seems a perfectly legitimate way to say that any of these elements
may have IDs named id.

It can't be just because XML DTDs don't have name classes, surely?
After all, DTD Compatibility allows multiple ID-type attributes on
a single element, which is neither XML- nor SGML-DTD compatible.

Now that Jing enforces this, I seem to have the choice of unfolding all my
name-class element patterns into choices of singleton-name elements,
or using the -i switch forevermore.

-- 
John Cowan           http://www.ccil.org/~cowan              cowan@ccil.org
To say that Bilbo's breath was taken away is no description at all.  There
are no words left to express his staggerment, since Men changed the language
that they learned of elves in the days when all the world was wonderful.
        --_The Hobbit_