Retrieves the revision's schema, conforming to JSON Schema.
	 *
	 * @since 4.7.0
	 *
	 * @return array Item schema data.
	 */
	public function get_item_schema() {
		if ( $this->schema ) {
			return $this->add_additional_fields_schema( $this->schema );
		}

		$schema = array(
			'$schema'    => 'http://json-schema.org/draft-04/schema#',
			'title'      => "{$this->parent_post_type}-revision",
			'type'       => 'object',
			// Base properties for every Revision.
			'properties' => array(
				'author'       => array(
					'description' => __( 'The ID for the author of the revision.' ),
					'type'        => 'integer',
					'context'     => array( 'view', 'edit', 'embed' ),
				),
				'date'         => array(
					'description' => __( "The date the revision was published, in the site's timezone." ),
					'type'        => 'string',
					'format'      => 'date-time',
					'context'     => array( 'view', 'edit', 'embed' ),
				),
				'date_gmt'     => array(
					'description' => __( 'The date the revision was published, as GMT.' ),
					'type'        => 'string',
					'format'      => 'date-time',
					'context'     => array( 'view', 'edit' ),
				),
				'guid'         => array(
					'description' => __( 'GUID for the revision, as it exists in the database.' ),
					'type'        => 'string',
					'context'     => array( 'view', 'edit' ),
				),
				'id'           => array(
					'description' => __( 'Unique identifier for the revision.' ),
					'type'        => 'integer',
					'context'     => array( 'view', 'edit', 'embed' ),
				),
				'modified'     => array(
					'description' => __( "The date the revision was last modified, in the site's timezone." ),
					'type'        => 'string',
					'format'      => 'date-time',
					'context'     => array( 'view', 'edit' ),
				),
				'modified_gmt' => array(
					'description' => __( 'The date the revision was last modified, as GMT.' ),
					'type'        => 'string',
					'format'      => 'date-time',
					'context'     => array( 'view', 'edit' ),
				),
				'parent'       => array(
					'description' => __( 'The ID for the parent of the revision.' ),
					'type'        => 'integer',
					'context'     => array( 'view', 'edit', 'embed' ),
				),
				'slug'         => array(
					'description' => __( 'An alphanumeric identifier for the revision unique to its type.' ),
					'type'        => 'string',
					'context'     => array( 'view', 'edit', 'embed' ),
				),
			),
		);

		$parent_schema = $this->parent_controller->get_item_schema();

		if ( ! empty( $parent_schema['properties']['title'] ) ) {
			$schema['properties']['title'] = $parent_schema['properties']['title'];
		}

		if ( ! empty( $parent_schema['properties']['content'] ) ) {
			$schema['properties']['content'] = $parent_schema['properties']['content'];
		}

		if ( ! empty( $parent_schema['properties']['excerpt'] ) ) {
			$schema['properties']['excerpt'] = $parent_schema['properties']['excerpt'];
		}

		if ( ! empty( $parent_schema['properties']['guid'] ) ) {
			$schema['properties']['guid'] = $parent_schema['properties']['guid'];
		}

		$schema['properties']['meta'] = $this->meta->get_field_schema();

		$this->schema = $schema;

		return $this->add_additional_fields_schema( $this->schema );
	}

	/**
	 * Retrieves the query params for collections.
	 *
	 * @since 4.7.0
	 *
	 * @return array Collection parameters.
	 */
	public function get_collection_params() {
		$query_params = parent::get_collection_params();

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

		unset( $query_params['per_page']['default'] );

		$query_params['exclude'] = array(
			'description' => __( 'Ensure result set excludes specific IDs.' ),
			'type'        => 'array',
			'items'       => array(
				'type' => 'integer',
			),
			'default'     => array(),
		);

		$query_params['include'] = array(
			'description' => __( 'Limit result set to specific IDs.' ),
			'type'        => 'array',
			'items'       => array(
				'type' => 'integer',
			),
			'default'     => array(),
		);

		$query_params['offset'] = array(
			'description' => __( 'Offset the result set by a specific number of items.' ),
			'type'        => 'integer',
		);

		$query_params['order'] = array(
			'description' => __( 'Order sort attribute ascending or descending.' ),
			'type'        => 'string',
			'default'     => 'desc',
			'enum'        => array( 'asc', 'desc' ),
		);

		$query_params['orderby'] = array(
			'description' => __( 'Sort collection by object attribute.' ),
			'type'        => 'string',
			'default'     => 'date',
			'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;
	}
}