SubjectAttributeDesignator question

How does one programmatically access the xml attributes of the
SubjectAttributeDesignator element?  The SubjectAttributeDesignator is
a subelement of the SubjectMatch element in an xacml policy target, as
shown in the policy fragment below:

	 
	  <Target>
	    <Subjects>
	      <Subject>
	        <SubjectMatch
	
MatchId="urn:oasis:names:tc:xacml:1.0:function:string-equal">
	          <AttributeValue 
	            DataType=http://www.w3.org/2001/XMLSchema#string
	              >employee</AttributeValue>
	          <SubjectAttributeDesignator 
	            AttributeId="group" 
	
DataType="http://www.w3.org/2001/XMLSchema#string"/>
	        </SubjectMatch>
	      </Subject>
	      ...
	   </Target>
	 
	The subject attribute value is available from an EvaluationCtx
by calling (as an example):
	  getSubjectAttribute(new
URI(com.sun.xacml.attr.X500NameAttribute.identifier), new
URI("urn:oasis:names:tc:xacml:1.0:subject:subject-id"), 
	    new
URI("urn:oasis:names:tc:xacml:1.0:subject-category:access-subject"))
	 
	But, it's not evident how to access the
SubjectAttributeDesignator.
	 
	Thanks,
	Dan Lanz