State channels: Produce when a new child is attached and if the size changes. In org.widok.Opt the size is reset if the value is cleared.,
Channels: The size is only produced in response to each received value on the channel.,
Buffers: Produce the row count once a row is added or removed.
Partial channels: Produce true if the current value is cleared.,
Channels: Produce false with the first received value.,
Buffers: Produce a new value once a row is added or removed.
Negation of isEmpty