Interface PlannerLevel is the base interface for {@link DebugLevel} and {@link AssertionLevel} enum types.
It should be noted that all enum implementations of this interface must declare a NONE or equivalent instance. This special case type tells the {@link cascading.flow.planner.FlowPlanner} to remove all {@link PlannedOperation} instances fromthe final {@link cascading.flow.Flow}.
@see DebugLevel
@see AssertionLevel