3.4. IPv6 Loopback Address and Other Format Prefixes

The loopback address MUST be treated as having link-local scope (Section 4 of [RFC4007]) and "preferred" (in the RFC 4862 sense) configuration status.

NSAP addresses and other addresses with as-yet-undefined format prefixes MUST be treated as having global scope and "preferred" (in the RFC 4862) configuration status. Later standards might supersede this treatment.