In the Webel recipe for pragmatic SE with SysML the custom Stereotype keyword «whitebox» applied to an Activity indicates that it is part of the functional analysis breakdown serving a «whitebox» «scenario» Activity (directly or indirectly) for a UseCase.
Note that «whitebox» refers here to the 'behavior' of a CallBehaviorAction even if it "shines" through as a so-called secondary stereotype on a CallBehaviorAction symbol in a «blackbox» level diagram!
The «whitebox» content is not somehow exposed here in the «blackbox» diagram; you have to navigate to the Activity Diagram for the «whitebox» Activity to see inside it as shown here with allocation swimlanes:
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