Wraps given partial sub in a {@link Subscription} and attaches it as child subscription. If opts defines a transducer (via xform key), input values will be transformed first before reaching the child sub's {@link ISubsciber.next} handler. Any further downstream subscriptions attached to the returned wrapped sub will also only receive those transformed values.
Removes given child sub, or if sub is omitted, detaches this subscription itself from its upstream parent (possibly triggering a cascade of further unsubscriptions, depending on {@link CommonOpts.closeOut} settings of parent(s)).
This logger's configured minimum log level