schema:             SCHEMA-SCHEMA
ref:                nx3.schema
dir-name:           schema
primary-key:        inetnum  cidr
primary-key:        inet6num cidr
primary-key:        role     nic-hdl
primary-key:        person   nic-hdl
owners:             mntner
key:                schema           required single   primary schema > [name]
key:                ref              required single   > [schema]
key:                primary-key      optional multiple > [schema] [key]
key:                dir-name         required single
key:                owners           optional single   > [schema]
key:                mnt-by           required multiple   lookup=nx3.mntner > [mntner]
key:                remarks          optional multiple > [text]...
key:                source           required single     lookup=nx3.registry
key:                network-owner    optional multiple > [parent-schema]
key:                key              required multiple > [key-name]
                    {required|optional|recommend|deprecate}
                    {single|multiple} {primary|} {schema|}
                    lookup=str '>' [spec]...
mnt-by:             NX3-MNT
source:             NX3
remarks:            # option descriptions
                    Attribute names must match /[a-zA-Z]([a-zA-Z0-9_\-]*[a-zA-Z0-9])?/.
                    required
                    :    object required to have at least one
                    optional
                    :    object not required to have at least one
                    single
                    :    only one of this type allowed
                    multiple
                    :    more than one of this type allowed
                    primary
                    :    use field as lookup key for lookup
                    * only one allowed per schema
                    * does not allow newlines
                    schema
                    :    use field name as the name of the schema
                    * only one allowed per schema
                    * does not allow newlines
                    lookup
                    :    schema match to use for related record
                    \> option specs
                    :    defines the option specifications for the key.
                    * must come last in option list
                    [label] string value. A positional string argument required.
                    Text inside brackets represent a label for the string and must match the same rules as attribute names.
                    If follwed by '...' values are gathered as an array.
                    {enum1|enum2|} enumeration. One option in pipe('|') deliniation is allowed.
                    If there is a trailing pipe it means the enum is optional. Enum values must match the same rules as attribute names.
                    'literal' Literal value. literal text value which must not contain any whitespace or single quotes.