Optionalplaceholder?: booleanOptionalreplace?: booleanWhen true, causes the previous hint to be replaced with this hint when
it is displayed.
When false, the previous hint remains visible when this one is
displayed. This allows for hints that build upon each other.
The UI needs to know how many hints there are before we have answerful PerseusItems. In a crunch, we decided to replace existing hints with empty hints and add a placeholder flag to signal that they're not real hints.
TODO(LEMS-3806): there's probably a better way to do this