Really, there is only one exception to the rule. You _ALWAYS_ validate your
ticket when you board trams, buses or enter a Railway station. The only
exception is when you buy a ticket on a tram, it is already validated. IMHO
they should allow you (but not require it) to validate on the tram after
you have just bought, to remove that exception. At the moment, it just says
"PASSBACK" if you try; a meaningless message in the circumstances. If they
made that change, the dumb user could just be told, "always validate",
while the smart user would notice that there was no need in the
tram-bought-ticket case.
Regards,
Mike Alexander
(malex@bigfoot.com)