The ids of the shown features that have an event state, by state: what setEventState and
user interactions have put, and clearEventState(s) hasn't taken off yet.
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 that have an event state, by state: what
setEventStateand user interactions have put, andclearEventState(s)hasn't taken off yet.