The ids of the shown features grouped by event state, as set by setEventState or user
interactions and not yet cleared by clearEventState(s).
Remarks
A state no feature has is absent rather than an empty array. The ids are those
ByIdOrIndex takes, so each can go straight back into setEventState or clearEventState.
The ids of the shown features grouped by event state, as set by
setEventStateor user interactions and not yet cleared byclearEventState(s).