Question: disjointness of classes and datatypes

All,

Hopefully a simple question:

The March 2001 reference description of DAML+OIL 
(http://www.daml.org/2001/03/reference.html) says

"Objects and Datatype Values - DAML+OIL divides the universe into two
disjoint parts. One part consists of the values that belong to XML
Schema datatypes. This part is called the datatype domain. The other
part consists of (individual) objects that are considered to be members
of classes described within DAML+OIL (or RDF). This part is called the
object domain."

However, this disjointness is not expressed in the language
specification of DAML+OIL (http://www.daml.org/2001/03/daml+oil.daml) as
far as I can see.

Is there a reason for this? How should a resource that claims to be an
instance or subclass of both daml:Class and daml:Datatype be handled -
the reference description says this is illegal but the language spec
doesn't. 

Also, is it illegal to explicitly declare a resource to be of type
daml:Datatype?

Regards,

David Allsopp
QinetiQ
UK

-- 
/d{def}def/u{dup}d[0 -185 u 0 300 u]concat/q 5e-3 d/m{mul}d/z{A u m B u
m}d/r{rlineto}d/X -2 q 1{d/Y -2 q 2{d/A 0 d/B 0 d 64 -1 1{/f exch d/B
A/A z sub X add d B 2 m m Y add d z add 4 gt{exit}if/f 64 d}for f 64 div
setgray X Y moveto 0 q neg u 0 0 q u 0 r r r r fill/Y}for/X}for showpage