document /nic/delete dyndns2 api extension

docs/standards.rst

@@ -10,3 +10,20 @@ Standards used
 * Backend: dynamic DNS update
 
   + `RFC2136 <http://www.ietf.org/rfc/rfc2136.txt>`_
+
+
+Extensions we made to the standards
+===================================
+
+/nic/delete API url
+-------------------
+
+The dyndns2 standard does not give a means to delete a DNS record (like A or
+AAAA), you can only update to a new address using /nic/update.
+
+Thus, we created a /nic/delete URL that behaves just like the dyndns2 update
+api, but removes the A or AAAA record in DNS instead of updating it.
+
+While the update API would actually use the given IP address to put it into
+an A or AAAA record, the delete API uses it only to determine the address
+type, whether it is IPv6 or v6 and then deletes the A or AAAA record.