The soap namespace prefix in your case is simply a shorthand for the real namespace URI. To avoid using http://soap/envelope/ everywhere, you can define once when soap means http://soap/envelope/ , and use soap in the rest of the document.
This means that if you use a namespace prefix, you must define it so that you can find the real namespace.
You can also declare that pizza matches http://soap/envelope/ and use this instead. The soap space prefix is not special.
Sjoerd
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