Parses the *rpc-reply*.

def parse(self):
        "Parses the *rpc-reply*."
        if self._parsed: return
        root = self._root = to_ele(self._raw) # The <rpc-reply> element
        # Per RFC 4741 an <ok/> tag is sent when there are no errors or warnings
        ok = root.find(qualify("ok"))
        if ok is None:
            # Create RPCError objects from <rpc-error> elements
            error = root.find('.//'+qualify('rpc-error'))
            if error is not None:
                for err in root.getiterator(error.tag):
                    # Process a particular <rpc-error>
                    self._errors.append(self.ERROR_CLS(err))
        self._parsing_hook(root)
        self._parsed = True