> I tried this and, as you know, it works. Amazing. I would *never* have
> expected an attribute named "exclude-result-prefixes" to, as it were,
> affect the way the source tree is perceived in match/select expressions;
> literal result elements, yes, but not match/select expressions.

no try it without exclude-result-prefixes. It will still work, it is
just that then the namespace declaration will appear in the result.

There is nothing special about the "default" namespace   it isn't really
a default at all it is just the same as any other binding except that
the prefix is empty and in that case the syntax is modified and you
ommit the :.