Webel: SysML: SE: Stereotype keyword convention: BY DEFINITION HERE «blackbox» and «whitebox» refer specifically to the 'problem' zone and NEVER the 'solution' zone (as opposed to more general uses of the terms 'black-box' and 'white-box').
Webel: SysML: SE: Terminology: '«logical» handler' is used for a specific kind of «logical» subsystem (aka 'conceptual subsystem') that is a SPECIFIC collaboration of parts that handle one Activity usage in a higher level «whitebox» Activity.
HOWTO "cheat" with two-level white-boxing and tracking stereotypes because you just don't want that darn "extra" logical subsystem (conceptual subsystem) Block the systems engineers reckon you are supposed to use (and why it's easier to actually use one)