Annotation issue: constraints on pattern with a:attributeType

[James Clark <jjc@jclark.com>]

If an <attribute> element has an a:attributeType annotation, what 
restrictions if any should be placed on the <attribute>'s pattern?

At the moment, the spec doesn't place any restrictions. Possible 
restrictons include:

(a) Disallow <text/>
(b) Disallow any <data> or <value> element with a datatype that has a 
different equality function from the builtin token datatype
(c) Disallow any <data> element that does not allow anything that is a 
legal XML name
(d) Disallow any <value> element specifying a value that is not a legal XML 
name

The problem with (b) is that it presents an implementation difficulty.  A 
datatype library will typically provide a method that checks instances of 
the datatype for equality.  But there's no way to tell whether that method 
is equivalent to the equality function for the builtin token function.  I 
guess datatype libraries would have to provide an additional method which 
says whether the equality function behaves like token for all values of the 
datatype.  Another complication is that the pattern may use <list> in the 
a:attributeType="IDREFS" case.

(c) also presents implementation difficulties (especially if there are 
regex parameters).

James