Has anyone considered having a canonical ASN.1 based format, and a
requirement that it be used if the record is over a certain set size? A
mapping of an XML schema into ASN.1 is quite possible.
It would allow simple setups to be textual and more complex ones to be
reduced in size. I believe detection could be as simple as checking
whether the first octet is an ASCII '<' or not.
ASN.1 is an ITU standard for binary tree structures, and is used in many
protocols specified in RFCs.
I think it might just be the thing needed, since gzipped XML is still
too large for DNS packets.
I must say I have some fondness for the SPF syntax, but I'd be quite
happy to simply have a way to compactly specify the XML-based variant.
Ari