async def on_raw_cap(self, message):
        """ Handle CAP message. """
        target, subcommand = message.params[:2]
        params = message.params[2:]

        # Call handler.
        attr = 'on_raw_cap_' + pydle.protocol.identifierify(subcommand)
        if hasattr(self, attr):
            await getattr(self, attr)(params)
        else:
            self.logger.warning('Unknown CAP subcommand sent from server: %s', subcommand)
Handle CAP message.