[tz] Getting close to new release: testing, testing, ...

[Zefram]

random832 at fastmail.us wrote:
>My thinking is, If it's not going to actually be compatible with current
>implementations, what's the point of being compatible at all?

Much less change is required to cope with the extended format than would
be required to cope with a new format.  I'm going to have to make such
code changes myself: my tzfile-parsing Perl module will reject '3' for
the version byte.  (It does so because it wasn't obvious, at version 2,
in what manner future changes to the format would be signalled, nor to
what extent they'd maintain compatibility.  Indeed, along with accepting
'3' I'll have to change the way the POSIXish-TZ field is processed.)

>I had been thinking about a PNG-like "chunk" structure  which would
>allow implementations to ignore anything they don't understand.

Yes, PNG's chunk system is a good model.  More generally, a new format
should have a well-defined extension mechanism, letting parsers know
which parts they need to understand and letting them skip the inessential
parts without understanding them.

-zefram