how to tell which subject has a permission of a role

Hi,

In BRAC profile of XACML v2.0, it defines HasPrivilegesOfRole <Policy> to tell which subject has a permission of a role. I reviewed the examples included in the profile for HasPrivilegesOfRole. But I did not find any where the examples tell who is the subjects, such as define subject match rules against subject's attributes. Could someone please explain how the HasPrivilegesOfRole <Policy> is defined and gives some examples to clarify it usage.

thanks

hao