Virtuoso XQuery uses some syntax extensions. Most visible is an
additional notation for qualified names as described above (name is
surrounded by "(!...!)" delimiters. An earlier implementation
allowed single-line comments started with "#" or "--" continuing to
the end of line, this syntax is now obsolete.
The "default namespace declaration" clause is not currently
supported, to make the text of XQuery unambiguous. If used, default
namespaces must extend element names but not attribute names.
Extension function names must be extended as they have non-default
namespace prefixes but the names of basic functions should not be
extended by the default namespace. Finally, Virtuoso will not
preserve any information about used namespace prefixes, so default
namespaces will be converted into non-default when the resulting
XML entity is printed.