I disagree with some of Paul Prescod's notions about XML and Web services. In particular, I'm not sure how much of REST applies to the "real" Web. In fairness though, I have to say that I haven't completely made up my mind on this.

On one notion though, I am in complete agreement: SOAP Encoding and SOAP RPC are hard for interop.

Also, he says that optional features in a spec are bad, because of interop. Again, I agree completely. A good spec says MUST or MUST NOT. MAY and SHOULD are usually compromises that do nothing for interop. There are exceptions to this rule, but not many.

Interop = mandatory features.