Return (prefixed) node name of `stmt`.

        The result is prefixed with the local prefix unless we are
        inside a global grouping.

def qname(self, stmt):
        """Return (prefixed) node name of `stmt`.

        The result is prefixed with the local prefix unless we are
        inside a global grouping.
        """
        if self.gg_level: return stmt.arg
        return self.prefix_stack[-1] + ":" + stmt.arg