An expression that identifies a button by name, number, or id, using one of the following forms:

card.buttonID(posInteger)

card.button(text)) // name

card.button(posInteger) // number

background.buttonID(posInteger)

background.button(text)) // name

background.button(posInteger) // number

For example:

thisCard.buttonID(3)

thisCard.button("Return")

thisCard.button(1)

thisBackground.button(2)