revised substitute text for section 5.6.1

The Policy Framework provides two modes of authoring policy expressions:
compact and normal form. One of the mechanisms that the Policy Framework
provides to policy authors for purposes of writing compact policy 
expressions is the wsp:Optional attribute. Assertion Authors should allow 
for the use of the wsp:Optional attribute in the XML outline and/or schema 
definition of an assertion as this will allow policy expression authors to 
compose compact policy expressions.

Best Practice 16: Assertion Authors should allow use of wsp:Optional 
attribute

An assertion's XML outline and/or schema definition should allow the use 
of the wsp:Optional attribute so as to enable policy authors to compose 
compact policy expressions.

For example, consider the following two equivalent policy expressions:

Normal form expression:

<wsp:Policy>
  <wsp:ExactlyOne>
    <wsp:All>
      <foo:Bar/>
    </wsp:All>
    <wsp:All>
    </wsp:All>
  </wsp:ExactlyOne>
</wsp:Policy>

Compact form expression:

<wsp:Policy>
  <foo:Bar wsp:Optional="true"/>
</wsp:Policy>

If the assertion author had not provided for the wsp:Optional attribute to 
be included on the assertion, then policy expression authors would be 
forced to use the more verbose normal form when including assertions of 
that type in their policies.

Cheers,

Christopher Ferris
STSM, Software Group Standards Strategy
email: chrisfer@us.ibm.com
blog: http://www.ibm.com/developerworks/blogs/page/chrisferris
phone: +1 508 234 2986