Okay. I think I fall in a slightly different place here, as I think
it would have
the same meaning with MARID contexts as the other parts do, and
that reusing the character for substructure would make sense. That
is opaque to IANA doesn't mean it needs to be opaque to the
application.
My understanding is rather that, yes, it does: so far as XML is
concerned, there simply isn't any internal structure to an XML namespace
URI for an application to be non-opaque to.
Bob