[dns-operations] underline in TXT's host

[Feng He]

Hello,

does the TXT record allow a underline in its hostname?
I see google does.

$ idig _spf.google.com txt
_spf.google.com.        300     IN      TXT     "v=spf1 
include:_netblocks.google.com include:_netblocks6.google.com ?all"


Thanks.