ignoring incorrect nameservers in authority section

[pyh at mail.nsbeta.info]

Sunil Shetye writes: 

> Quoting from pyh at mail.nsbeta.info's mail on Thu, Dec 30, 2010:
>> What's the difference between these two flags in the response of
>> dig? 
>> 
>> < ;; flags: qr ra; QUERY: 1, ANSWER: 1, AUTHORITY: 2, ADDITIONAL: 0
> 
> ra : recursion available
>     The nameserver is ready to ask other nameservers for the record we
>     queried. 
> 
> As the 'aa' flag is also missing above, the answer is not authoritative. 
> 
>> >;; flags: qr aa; QUERY: 1, ANSWER: 1, AUTHORITY: 2, ADDITIONAL: 0
> 
> aa : authoritative answer
>     The nameserver is authoritative for the zone of the record that we
>     queried. 
> 
> As the 'ra' flag is also missing above, the nameserver will not do a
> lookup for you for records it does not know about. 
> 

Thanks a lot.
Where is the document for these flags?
I google'd but got no correct result :) 

Regards.