background owners

[Wilhelm Sanke]

Is there a quick way to know which of a stack`s backgrounds (groups with
background behavior set to true) are on no card?

Background owners can be

- another group
- a card
- the stack itself

The problem is that for backgrounds on *unvisited* cards the owners are
returned as "stack" even when the real owner is the card.

A workaround is to first go to all cards of a stack - and only after
that ask for the owners of backgrounds - but this takes extra seconds
for large stacks on slower computers (about two seconds for stacks with
1000 cards on a computer with 800 MHz on Windows).

Is there a direct way to determine which backgrounds are on no card at
all?

Regards,

Wilhelm Sanke