sealedFamily

This class and, where it is sealed, every class below it - through sealed classes all the way down.

A codec decodes to one concrete class, and a value is looked up by its own class: PgInterval.Finite, never PgInterval. So what is registered under a sealed class is indexed under each of these, which keeps every lookup an exact one. A class below one that is open rather than sealed cannot be listed, and is not.

Cached for good, being asked again for every execution that carries converters of its own.