Several opportunities for clarification in the description of the portTypes

In section 13.1:

 * "All of the member Grid service instances of a ServiceGroup MUST conform to 
(ie be a subtype of) one of the portTypes..."
  > should be "at least one of..." (see 13.1.1 paragraph 1)

 * "The content element of the Entry SDE SHOULD include all the ContentTypes 
for all the memberInterfaces listed in the membershipContentRule,..."
  > should be "for any memberInterfaces that the entry's member service 
implements." (see 13.1.1 paragraph 1.)

 Better still, remove this duplication of these rules in favour of 13.1.1 para 
1.

Section 13.2:

  * paragraph 1, 2nd sentence "Each ServiceGroupEntry service..." 
    should be "Each ServiceGroupEntry service instance..."
 
Section 13.2.2

  * 2nd sentence. "..(where the destruction of the ServiceGroupEntry removes 
the member service..."

    - "..destruction of the ServiceGroupEntry service instance.."      
    - clarify "removes" with "MUST" or "SHOULD" remove...  
    - "..the member service instance 'entry' data element."

Section 13.3.2.2

  * Input parameter description, penultimate sentence. "..this is equivalent to 
performing a destroy operation on the matching ServiceGroupEntry services."

    - Clarify the coherency rule between ServiceGroup 'entry' SDE elements and 
the corresponding ServiceGroupEntry instance.
 .