// (12,13): error CS8652: The feature 'index operator' is currently in Preview and *unsupported*. To use Preview features, use the 'preview' language version.
// (13,13): error CS8652: The feature 'index operator' is currently in Preview and *unsupported*. To use Preview features, use the 'preview' language version.
// (14,13): error CS8652: The feature 'index operator' is currently in Preview and *unsupported*. To use Preview features, use the 'preview' language version.