[Arnt]

But Jon Postel didn't mean what people now think he did.

His famous principle is about border cases, when the spec is vague, handwavy or thought by some to be vague. It's not about the other cases.

Remember that Jon Postel was the RFC editor. He didn't want anyone to ignore the RFCs, he wanted the RFCs to be readable and pleasant, and he wanted implementers to do the right thing when when an RFC erred on the side of readability.

FWIW I wrote a blog post about this a few years ago, http://rant.gulbrandsen.priv.no/postel-principle

[nly]

Here's an example of the problem with that though: a mailing[0] by someone in February of this year asking if there's a formal grammar for the DNS zone (master) file format. This is a format that was first loosely specified in a RFC almost 32 years ago and there still isn't a rigorous definition. BIND now specifies a defacto interpretation with lots of liberal "treat this as a warning" options[1] and new gTLDs registries now insist on a subset of the original specification.

HTTP also has corner cases that widely-used implementations simply aren't handling consistently because the original RFCs are vague or the ideas being conveyed are buried in even older RFCs that nobody has the incentive to drill in to, or simply aren't known to them.

IMHO the IETF really should move to a wiki format, where information and wording changes on a particular protocol can be seen in one place. Plaintext snapshots of particular versions could still be published.

[0] https://www.ietf.org/mail-archive/web/dnsop/current/msg13349...

[1] https://kea.isc.org/wiki/ZoneLoadingRequirements#a3.3RFCimpl...

[Arnt]

BTW there's a reason for that. The IETF decided (it must be a couple of decades ago) to restrict itself to matters of the internet. Things like file formats are thus out of scope for RFCs. There have been exceptions, RFC5952 is a good example and I know at least two others, but by and large RFCs are about the internet now, not about file formats or other worthy subjects.

[Alupis]

RFC 6120 and 6121 are for XMPP (chat), and define XML is to be used, and even goes into the exact structure of the XML "packets".

[zeen]

Bad example. XML is the wire format in XMPP RFCs, not a file format.

[nly]

RFC7159? It even recommends a file extension.

[Arnt]

That's a perfect example: Publishable as an RFC because the format is used in many APIs on the general internet, but also says a little about a local matter, in this case the file names.

Is the rule a bit messy? Yes it is!

[zdw]

There's a reason why I try to use the tinydns zonefile format (http://cr.yp.to/djbdns/tinydns-data.html) whenever I can.

It's so much simpler to use, and less problematic.