Source

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

public function get_collection_params() {
		$types    = array();
		$subtypes = array();

		foreach ( $this->search_handlers as $search_handler ) {
			$types[]  = $search_handler->get_type();
			$subtypes = array_merge( $subtypes, $search_handler->get_subtypes() );
		}

		$types    = array_unique( $types );
		$subtypes = array_unique( $subtypes );

		$query_params = parent::get_collection_params();

		$query_params['context']['default'] = 'view';

		$query_params[ self::PROP_TYPE ] = array(
			'default'     => $types[0],
			'description' => __( 'Limit results to items of an object type.' ),
			'type'        => 'string',
			'enum'        => $types,
		);

		$query_params[ self::PROP_SUBTYPE ] = array(
			'default'           => self::TYPE_ANY,
			'description'       => __( 'Limit results to items of one or more object subtypes.' ),
			'type'              => 'array',
			'items'             => array(
				'enum' => array_merge( $subtypes, array( self::TYPE_ANY ) ),
				'type' => 'string',
			),
			'sanitize_callback' => array( $this, 'sanitize_subtypes' ),
		);

		return $query_params;
	}