daylight saving time algorithm changing

[Rick DeNatale]

So my curiosity is piqued. I tried to figure out what the format of
the timezone data files is. Googling various things failed to turn up
any documentation on what is inside these files.

Does anyone know where they are documented?  Is it possible that they
can descibe not only what the rules for dst are in a particular
timezone, but also that the rules are x now and they change to y on
such and such a date?