This looks like like RCS keywords, which are used also by other version control systems, such as CVS or Subversion:

http://svnbook.red-bean.com/en/1.7/svn.advanced.props.specia...

I... I don't know why would anyone put one in a TXT record. It's likely a mistake.

The other example domains (example.org, example.net) don't have such record.

If you are managing your zone data in RCS or similar, why not expose that information in DNS as well? Could be useful for debugging.

Indeed, on 2015-01-01, it said "$Id: example.com 3280 2014-12-10 00:15:12Z spowell $".

It does not look like a mistake to me.

Thanks for your input, I think you're right – it's deliberate, but seems like a pretty wasteful use of DNS TXT to me. Every SPF lookup is dragging that much bigger record with it too and it serves no real purpose for anyone other than the administrators of the example.com zone. It seems like a strange thing to put in this zone particularly because it's used in so many examples.

I bet this was in before the SPF also went in. You should feel free to take this up with IANA, of course :)

Thank you for your reply and the link. That's very helpful and I agree this looks like the explanantion.

Do you know of a definitive list anywhere that shows the different uses made of DNS TXT records?

I know Google and plenty of others use them for domain verification but I'm more interested in protocols like SPF, DKIM and DMARC but I've been unable to find a list. (edit: added missing word)

Also, a link I found for using RCS to track DNS changes:

https://www.techrepublic.com/blog/linux-and-open-source/how-...