'Do some simple checking of the zone\'s origin.
@raises dns.zone.NoSOA: there is no SOA RR
@raises dns.zone.NoNS: there is no NS RRset
@raises KeyError: there is no origin node'

def check_origin(self):

    if self.relativize:
        name = dns.name.empty
    else:
        name = self.origin
    if (self.get_rdataset(name, dns.rdatatype.SOA) is None):
        raise NoSOA
    if (self.get_rdataset(name, dns.rdatatype.NS) is None):
        raise NoNS
