[tz] What is LMTZ?

[Paul Eggert]

Lester Caine wrote:
> I'd almost argue that NO historic data is better than a SINGLE subset arbitrarily selected?
> Currently there is no mechanism to tell you that the historic data may not actually apply at all?

These are both valid points.  It's certainly easy to
remove data before 1970 automatically, and some platforms
do that now (QNX, for example), so the first option is
already there and some platforms already take it.

As for the second, we could add a comment to each
zone specifying the earliest time stamp such that
the zone is known to be valid for all locations
in its region after that time.  The default would
be 1970, which means the tz database trivially
conforms to this pattern now.

I see two problems with this idea, though.  First,
it needs to be integrated with winnowing, and it's
not yet clear how that would work.  Second, and more
important, except for Europe/London and perhaps
a handful of other places, we wouldn't know what
value to put into the comment, other than
the default "1970".  This seems a fairly serious
objection.