tzdata format

[D. J. Bernstein]

Supposedly rule lines can occur in any order. What do the following
lines mean?

   Rule Silly 1999 only - Sep 3 5:00 2:00 X
   Rule Silly 1999 only - Sep 3 6:00 1:00 Y
   Rule Silly 1999 only - Sep 3 8:00 -3:00 Z

Starting from 0:00 +0000, do we increase to 5:00 +0000, then jump to
7:00 +0200, then increase to 8:00 +0200, then jump to 3:00 -0300, then
increase to 6:00 -0300, then jump to 10:00 +0100, then increase?

Or do we increase to 6:00 +0000, then jump to 7:00 +0100, then increase
to 8:00 +0100, then jump to 4:00 -0300, then increase to 5:00 -0300,
then jump to 10:00 +0200, then increase?

Why aren't transition times labelled with the starting offset? Or, more
simply, always specified in terms of standard time?

I see that Tunisia one year had two transitions in the same month. Why
are these part of the rule rather than the zone? Are there other
examples of two transitions in the same month?

Are there any DST systems that don't consist of two jumps in each
applicable year, one jump early in the year, one jump late in the year?
Are there any rule lines that cover multiple years without being part of
such a pair?

---Dan