From mAirListWiki

(introduced in mAirList 3.0.5)

Emergency actions are a certain set of actions inside an action list (for example, used for an event) which are executed only if one of the preceeding actions failed or reported an error.

For example. in an event which loads the current playlist from the database, you can add an emergency action which loads a backup playlist from a file instead. That action is only executed if there was an error fetching the playlist from the database.

Emergency actions are wrapped inside a special "action list container". To add emergency actions to a list of actions, click Add then Emergency action list to add the container. In the properties dialog of that container, you will find another action list editing pane where you can add the desired actions.