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
mnt-by:     XUU-MNT
mnt-by:     HEXA-MNT