One thought -- and perhaps this already exists -- is to introduce
@infoversion as the first tag that should appear in the input. This
Changes to the info format are few and far between. Changes to the
format that actually affect old document are even fewer -- I don't think
it's ever happened. There's no reason to make readers gratuitiously
barf on documents that happen to be generated with a new version of
makeinfo.
We could introduce backwards-compatible way of specifying a version
number, I suppose. This would not be high on my list.
