when
Registers an action to execute when an element becomes known. The action is only executed for those elements that are required. Fails if any element has already been finalized.
Parameters
action
The action to execute for each element becomes known.
Registers an action to execute when an element of the given type becomes known. The action is only executed for those elements that are required. Fails if any matching element has already been finalized.
Parameters
type
The type of element to select.
action
The action to execute for each element becomes known.