This action event can be used to show a hidden group. Optionally, a transition effect can be used.
When using a transition effect, you can also select the "Merge group objects into single effect" option. In that case all group objects will be combined into a single layer before the transition effect is shown so that the transition effect will be shown on the group as a whole instead of on the group members individually.
Groups can be hidden again by using the Hide group action event.