Hi!
First of all, this is the policy expression discussed:
The <All> element means that all contained policies are required (but it is not as simple, so read on!
).
The <mtom:OptimizedMimeSerialization> element says that MIME serialization is required, until we encounter the Optional attribute, which suddenly makes MIME serialization optional. Note that the Optional attribute only affects the MIME serialization policy!
The <wsam:Addressing> element says that addressing is required. Period.
The <log:Logging> element says that logging is required, until we see the Ignorable attribute with a value "true" which tells us that the requirement regarding logging may be ignored. Again, this only affects the policy element in which the Ignorable attribute appears, which is logging.
Then there is an <ExaclyOne> element, which means that exactly one of the policies contained in this element is required.
Hope this clarifies!
Best wishes!