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

card.fieldID(posInteger)

card.field(text)) // name

card.field(posInteger) // number

background.fieldID(posInteger)

background.field(text)) // name

background.field(posInteger) // number

For example:

thisCard.fieldID(3)

thisCard.field("My Notes")

thisCard.field(1)

thisBackground.field(2) // background field