[xacml] Multi-valued attributes in Request. Forwarded from SethProctor.

I'm looking for a clarification on the use of multiple AttribueValue entries
in an Attribute type in the Request. If I have an Attribute with multiple
AttributeValue entries, am I supposed to treat each of these as being
(effectively) separate Attributes with the same values for their meta-data?
This seems like the logical approach, but nothing in the spec defines the
right behavior. Following from this, is it an error if the Subject Category
(for instance) Attribute has multiple AttributeValue entries, since the spec
says that there must be one and only one value for this attribute?