John Levine wrote:
Same with the Clipper card used in the San Francisco area. *A card can have both
passes and a cash balance for trips not covered by any of the passes. *It works
on seven different transit systems and can handle a baffling array of passes and
discount plans. *You can have a Muni monthly pass, and a BART High Value Discount
ticket which gives you $64 of BART credit for $60, as well as passes on other
systems and cash.

Is BART credit stored separately from otehr agencies' credit?

In the NYC region, the 7% Metrocard bonus when you load at least $10
applies to the credit you can use on any agency that takes Metrocard.
I'm not sure how they "fund" the bonus. (Consider that a card could
have been loaded multiple times, sometimes with the bonus and
sometimes without, so it's hard to figure out how much real cash
revenue the card balance represents.)

Jimmy