'Cause the element to contain namespace declarations. By default, the
namespace prefixes defined in the Builder class are used. These can
be overridden by providing exlicit prefixes, e.g.
``with_nsdecls(\'a\', \'r\')``.'

def with_nsdecls(self, *nspfxs):

    if (not nspfxs):
        nspfxs = self.__nspfxs__
    self._nsdecls = (u'    %s' % nsdecls(*nspfxs))
    return self
