[tz] Beginner's help request

[Daniel Ford]

Thanks guys - you've all been extremely helpful, and I appreciate it.  I've
been trying to conceive an algorithm for finding the 'current' rules for a
locale, based on its 'reference city', and you've helped clarify what that
will involve, though I'm not there yet.

Thanks also for the pointer to Africa/Casablanca as one of the known
'4-transitions' localities.  And I liked the timeanddate visualisation,
Matt.  (Timeanddate has long been my 'goto' site for world time info and
calculators.)

So now I've opened the 'africa' file and searched for Africa/Casablanca, but
I only see *two* rules for 2017.  So how does the TZdb indicate that there
are *four* transitions this year?

Regards,
Daniel