In Section 3.7, Primer, only attribute extensibility is specified for PolicyReference element. This is inconsistent with Section 4.3.4 of the WS-PolicyFramework that allows both element and attribute extensibility for this element.

Primer, Section 3.7: 
(current) "The PolicyReference element allows attribute extensibility."

WS-Policy Framework, Section 4.3.4:
  /wsp:PolicyReference/{any}
   "Additional elements MAY be specified but MUST NOT contradict the
   semantics of the [parent element]; if an element is not recognized,
   it SHOULD be ignored."
  
Proposal for Change for Section 3.7, Primer:
 "The PolicyReference element allows element and attribute extensibility."