TXT & SPF Record Syntax

[Tim Daneliuk]

I am trying to understand when the LHS of a TXT record needs to be terminated with '.'.

For example, I see this one of the machines I am managing.  The server in question is
the zone authority for foo.com:

foo.com.             IN TXT "v=spf1 ...
foo.com.             IN SPF "v=spf1 ...
something._domainkey IN TXT "v=DKIM1 ...
_dmark.foo.com.      IN TXT "v=DMARC1 ...

Could some kind soul explain why the DKIM key name does not require the trailing period, but
why all the foo.com entries do?