CD-1 issue #48: bag from attribute assignment expression

The issue number refers to the XLS-sheet found in this email:
http://lists.oasis-open.org/archives/xacml/200909/msg00013.html

The comment proposes that bags should be allowed as the result of an 
attribute assignment expression.

Since this was my comment, naturally, I agree.

I propose that we change the specification so that if the attribute 
assignment expression evaluates to an atomic value, then the result is a 
single attribute assignment. And if the attribute assignment expression 
evaluates to a bag, then for each value in the bag there shall be an 
attribute assignment in the obligation/advice. If the bag is empty, then 
there shall be no attribute assignment corresponding to this attribute 
assignment expression.

Best regards,
Erik