',
			'enum'        => array(
				'date',
				'id',
				'include',
				'relevance',
				'slug',
				'include_slugs',
				'title',
			),
		);

		return $query_params;
	}

	/**
	 * Checks the post excerpt and prepare it for single post output.
	 *
	 * @since 4.7.0
	 *
	 * @param string  $excerpt The post excerpt.
	 * @param WP_Post $post    Post revision object.
	 * @return string Prepared excerpt or empty string.
	 */
	protected function prepare_excerpt_response( $excerpt, $post ) {

		/** This filter is documented in wp-includes/post-template.php */
		$excerpt = apply_filters( 'the_excerpt', $excerpt, $post );

		if ( empty( $excerpt ) ) {
			return '';
		}

		return $excerpt;
	}
}