[cedilla]

That's not true. The domain name system doesn't really know about different levels of domains, so such a rule doesn't even make that much sense.

What you are not allowed to have is a CNAME record in addition to anything else. So if you want a TXT or SRV or MX record, you can't also have the CNAME. Makes sense as the latter basically means "look here instead".

[Sophira]

While you're technically correct that the specification doesn't specifically say that you can't have a CNAME on the root domain, it is still true that you cannot have a CNAME on the root domain because DNS requires that you have SOA and NS records on the root domain, which means that a CNAME is not possible due to the rule you cite.