Apex domains cannot have CNAME records.
Question and response
Question
dig xenox.systems. NS
Answer
xenox.systems. 5 NS ns2.xenox-systems.net.
xenox.systems. 5 NS ns1.xenox-systems.net.
xenox.systems. 5 NS ns3.xenox-systems.net.
Authority
The response has no authority records.
Additional
ns1.xenox-systems.net. 5 A 213.239.242.238
ns2.xenox-systems.net. 5 A 213.133.105.6
ns3.xenox-systems.net. 5 A 193.47.99.3
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0