Source

File: wp-includes/rest-api/endpoints/class-wp-rest-search-controller.php

protected function get_search_handler( $request ) {
		$type = $request->get_param( self::PROP_TYPE );

		if ( ! $type || ! isset( $this->search_handlers[ $type ] ) ) {
			return new WP_Error(
				'rest_search_invalid_type',
				__( 'Invalid type parameter.' ),
				array( 'status' => 400 )
			);
		}

		return $this->search_handlers[ $type ];
	}