The soap:mustUnderstand attribute is a strange beast.

When soap:mustUnderstand="true" is present that header element must be understood by the receiving application.

Err? What's that mean, boss? Maybe:

• You reject all messages with header elements that you don't understand where the 'mustUnderstand' attribute is true.

• You see that there is a mustUnderstand attribute and ignore it. Maybe you understand it and maybe you don't. This is like punting on a test (e.g. answering "7" or "C" when you don't know).

• You don't look at the mustUnderstand attribute and so you lie and act like you understand it.

• You reject all messages with mustUnderstand because you can't understand mustUnderstand.