question: private static boolean addToEvaluator ( ArrayDeque < FilterValueSetParam > remainingParameters , FilterHandle filterCallback , EventEvaluator eventEvaluator , ArrayDeque < EventTypeIndexBuilderIndexLookupablePair > treePathInfo , FilterServiceGranularLockFactory lockFactory ) { if ( eventEvaluator instanceof FilterHandleSetNode ) { FilterHandleSetNode node = ( FilterHandleSetNode ) eventEvaluator ; addToNode ( remainingParameters , filterCallback , node , treePathInfo , lockFactory ) ; return true ; } FilterParamIndexBase nextIndex = ( FilterParamIndexBase ) eventEvaluator ; FilterValueSetParam parameter = IndexHelper . findParameter ( remainingParameters , nextIndex ) ; if ( parameter != null ) { remainingParameters . remove ( parameter ) ; treePathInfo . add ( new EventTypeIndexBuilderIndexLookupablePair ( nextIndex , parameter . getFilterForValue ( ) ) ) ; addToIndex ( remainingParameters , filterCallback , nextIndex , parameter . getFilterForValue ( ) , treePathInfo , lockFactory ) ; return true ; } return false ; }
target:  Add filter callback to an event evaluator, which could be either an index node or a set node.