[dns-operations] about the underline in hostname

[hua peng]

I found this is a valid RR:

_spf.yandex.ru.         2768    IN      TXT     "v=spf1
include:_spf-ipv4.yandex.ru include:_spf-ipv6.yandex.ru ~all"


But for A, CNAME, AAAA etc, the underline in hostname is invalid.
Does this make a confusion?

Thanks.