WP_REST_Attachments_Controller::get_collection_params

					'description' => __( 'Description for the object, as it exists in the database.' ),
					'type'        => 'string',
					'context'     => array( 'edit' ),
				),
				'rendered' => array(
					'description' => __( 'HTML description for the object, transformed for display.' ),
					'type'        => 'string',
					'context'     => array( 'view', 'edit' ),
					'readonly'    => true,
				),
			),
		);

		$schema['properties']['media_type'] = array(
			'description' => __( 'Attachment type.' ),
			'type'        => 'string',
			'enum'        => array( 'image', 'file' ),
			'context'     => array( 'view', 'edit', 'embed' ),
			'readonly'    => true,
		);