schema:             AS-BLOCK-SCHEMA
ref:                dn42.as-block
key:                as-block   required  single    primary schema
key:                descr      optional  single
key:                policy     required  single    > {open|ask|closed}
key:                mnt-by     required  multiple  lookup=dn42.mntner
key:                admin-c    optional  multiple  lookup=dn42.person,dn42.role
key:                tech-c     optional  multiple  lookup=dn42.person,dn42.role
key:                remarks    optional  multiple
key:                source     required  single    lookup=dn42.registry
mnt-by:             DN42-MNT
source:             DN42