AIs use priorities to decide which of their available actions to take. When using Pseudo-scripts or customizing Response actions, you need to choose an appropriate priority so that your custom actions will, for example, take place instead of the AI patrolling, but not stop the AI from being being stunned by flashbombs.
there is a fixed ranking for different types of actions
Stock AI actions have priorities as shown in the following table; higher actions will win out over lower actions in the same priority section. Note that no stock actions have Absolute priority.
Typically you should select the lowest effective priority for your chosen actions in the pseudoscript. For example, if your pseudoscript directs a patrolling AI to go to a location, you will need this to override their patrol behaviour. The lowest priority that outranks Patrol is Normal, so choose this.
Note that the Default/None priority for pseudoscript actions is Normal for AIWatchObj and Responses, but Low for Conversations.
Absolute priority should generally be avoided. It is usually inappropriate for AIs that the player interacts with; but is useful for off-screen helper AIs, to ensure they do only as their pseudoscripts direct.
When an AI chooses between actions at the same priority level, there is a hardcoded ranking so that some actions will always win out over others. For instance, an AI directed to Goto a location with Very High priority will interrupt that action in order to Die, due to this ranking.