card
Places the child on the card named key, the card the panel shows while its selectedCard equals that key. The name follows the value: a child declaring a new key moves to that card, keeping its position among its siblings.
key cannot be empty, and two children of one panel cannot name the same card; either is refused, and a card named twice is reported by its name.
Return
this chain with the card declared on it.
Parameters
key
names the card this child is placed on, non-empty