[ebxml-msg] Question about OPTIONAL

I am discussing the use of OPTIONAL modules with IIC, and I need to get a
question answered.

What do we want to do if, for instance, an AckRequested element is on the
message but the Receiving MSH does not support RM.  I see three options:

1)  Stop processing and send back an Error -- NotSupported/Error
2)  Continue processing but send back an Error -- NotSupported/Warning
3)  Ignore and continue processing (no error).

Since AckRequested has mustUnderstand="1", option 3 is not really an option
(unless we change).  I think business users would prefer that a PO goes on
through (option 2) and I am leery of stopping a message when there is no error
in the message so I don't really like option 1.

SOAP 1.1 section 4.2.3 SOAP mustUnderstand Attribute says:

. . .with a value of "1" the recipient of that header entry either MUST obey the
semantics (as conveyed by the fully qualified name of the element) and process
correctly to those semantics, or MUST fail processing the message. . .

Can we specify the behavior of option 2 with a value mustUnderstand="1"?

Thoughts?

Regards,

David Fischer
Drummond Group.