RFC compliance: MUST v SHOULD or MAY

[Lee]

As long as I'm asking ignorant questions.. is there some reason why
bind (at least as it came configured on my Debian machine) looks up
.local names?

I added this bit to named.conf to do what seemed reasonable.  But
again - it seems reasonable _to me_ I dunno if anyone else agrees & it
seems like either way is RFC compliant.

zone            "local"       in { type master; notify no; file
"/etc/bind/db.null"; };
    #   https://tools.ietf.org/html/rfc6762
    # This document specifies that the DNS top-level domain ".local." is a
    # special domain with special semantics, namely that any fully
    # qualified name ending in ".local." is link-local, and names within
    # this domain are meaningful only on the link where they originate.
    #
    # Any DNS query for a name ending with ".local." MUST be sent to the
    # mDNS IPv4 link-local multicast address 224.0.0.251 (or its IPv6
    # equivalent FF02::FB).
    #
    # Implementers MAY choose to look up such names concurrently via other
    # mechanisms (e.g., Unicast DNS) and coalesce the results in some
    # fashion.
    #
    # "ping mypc.local." does a normal dns lookup followed by a
    # link-local multicast name resolution to 224.0.0.252
    # adding local to null.zone at least stops the normal dns lookup


TIA,
Lee