* Every coroutine builder (like [launch][CoroutineScope.launch], [async][CoroutineScope.async], etc)
* and every scoping function (like [coroutineScope], [withContext], etc) provides _its own_ scope
* with its own [Job] instance into the inner block of code it runs.
* By convention, they all wait for all the coroutines inside their block to complete before completing themselves,
* thus enforcing the discipline of structured concurrency.