Spans started in the context of the provided callback will be children of this span. If null is passed,
spans started within the callback will not be attached to a parent span.
Execution context in which the provided span will be active. Is passed the newly forked scope.
the value returned from the provided callback function.
Forks the current scope and sets the provided span as active span in the context of the provided callback. Can be passed
nullto start an entirely new span tree.