Circular References in XACML PolicySets

Hi All,

I couldn't find an answer for this in the XACML spec:

Are cycles allowed in XACML PolicySet references?

For example, a PolicySet (PS) A refer  to a PS B, which in turn
references C which refers to A. Would this be legal in XACML?

Thanks,
Vladimir Kolovski
PhD Candidate, University of Maryland-College Park