def is_subdomain_record(rec):
    """
    Does a given parsed zone file TXT record (@rec) encode a subdomain?
    Return True if so
    Return False if not
    """
    txt_entry = rec['txt']
    if not isinstance(txt_entry, list):
        return False

    has_parts_entry = False
    has_pk_entry = False
    has_seqn_entry = False
    for entry in txt_entry:
        if entry.startswith(SUBDOMAIN_ZF_PARTS + "="):
            has_parts_entry = True
        if entry.startswith(SUBDOMAIN_PUBKEY + "="):
            has_pk_entry = True
        if entry.startswith(SUBDOMAIN_N + "="):
            has_seqn_entry = True

    return (has_parts_entry and has_pk_entry and has_seqn_entry)
Does a given parsed zone file TXT record (@rec) encode a subdomain?
    Return True if so
    Return False if not