[Section 2.3] Sequence number in singleton group

Section 2.3, Groups of Messages and Message Identity, states,
beginning at line 512:

   (1) In case there is only one message in the group (singleton): the
       group ID, which is a globally unique group identifier, may be
       used alone as Message Identifier. No sequence number is
       required, although allowed.

If a sequence number is allowed on a singleton group, the spec should
provide an example since it is not obvious what distinguishes such a
message from either a message that is one of a group of several
messages or a message that should produce an InvalidMessageId fault.

I.e., I suspect that this is valid, but I couldn't say for sure:

<MessageId groupId="mid:///">
  <SequenceNum number="0"/>
</MessageId>

It also seems to me that allowing SequenceNum on a singleton group
will requrie a lot of special-casing in the code that detects
InvalidMessageId faults, but it also seems to me that that is not a
sufficient reason in itself to disallow such message ID types.

Regards,


Tony Graham
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