By triggering a Theme you tell psai that some in-game-event occurred, that should generally initiate the playback of the given Theme. Such an event could be that the player has stepped into a certain area of your game world, or some event could be that (s)he has been attacked. Triggering a Theme does not necessarily result in the given Theme to be played back immediately, as there are Themes that have a higher priority than others. E.g. you don't want your furious battle music to be interrupted by some soft ambient Theme, just because the player has stepped into a forest during the battle. To achieve this priority-ranking, psai comes with seven pre-defined Theme Types, that define the basic playback behavior of a Theme.
Regardless of the Theme Type, each Theme will always start immediately upon a call to TriggerMusicTheme if no other Theme is playing at that moment. In any other case, psai will automatically decide if the playing Theme is interrupted or not, and if so, in what manner the transition to the new Theme should be achieved. As stated above, this decision is based on the Theme Types of the triggered Theme and the playing Theme. Please see the Table of Theme Types for the decision matrix.