Ticket 401: Specify whether instances of record types have external representations and are readable.

We should specify whether instances of record types have external representations, can be read back in, and can be included in quoted forms.

We should say that calling display', write', etc. on such objects is allowed, but that the printed representation is unspecified. It follows that reading them and using them in quoted forms should be implementation-dependent, too.

This suggestion is inspired by comments by Alexey Radul.