The nested workflow specifying the condition must return a sequence of type bool. This nested sequence may be synchronous or asynchronous with respect to notifications from the source sequence. After each element is emitted by the source sequence, the latest value from the nested sequence is checked. If the value is true then the element will be accepted and emitted by the result sequence. Otherwise, the element will be dropped.

As an example of asynchronous condition evaluation, it is possible to build a simple manual toggle by using a BooleanProperty connected directly to the output of the nested workflow: