public function messageFilterCallback( $key /*...*/ ) {
		$params = func_get_args();
		array_shift( $params );
		if ( count( $params ) == 1 && is_array( $params[0] ) ) {
			// Unwrap args array
			$params = $params[0];
		}
		$msg = $this->ctx->message( $key, $params );
		return $msg->plain();
	}