Event Definitions is the main tab and contains the key fields when working with action triggers. These fields include:
| Field | Description | 
| Owning Library | The shortname of the library for which the action / trigger / hook is defined. | 
| Name | The name of the trigger event, that links to a trigger event environment containing a set of fields that will be returned to the Validators and/or Reactors for processing. | 
| The name of the trigger for the trigger event. The underlying action_trigger.hook table defines the Fieldmapper class in the core_type column off of which the rest of the field definitions “hang”. | |
| Enabled | Sets the given trigger as enabled or disabled. This must be set to enabled for the Action trigger to run. | 
| Processing Delay | Defines how long after a given trigger / hook event has occurred before the associated action (“Reactor”) will be taken. | 
| Processing Delay Context Field | Defines the field associated with the event on which the processing delay is calculated. For example, the processing delay context field on the hold.capture hook (which has a core_type of ahr) is capture_time. | 
| Processing Group Context Field | Used to batch actions based on its associated group. | 
| Links the action trigger to the Reactor. | |
| The subroutines receive the trigger environment as an argument (see the linked Name for the environment definition) and returns either 1 if the validator is true or 0 if the validator returns false. | |
| Event Repeatability Delay | Allows events to be repeated after this delay interval. | 
| Failure Cleanup | After an event is reacted to and if there is a failure a cleanup module can be run to clean up after the event. | 
| Granularity | Used to group events by how often they should be run. Options are Hourly, Daily, Weekly, Monthly, Yearly, but you may also create new values. | 
| Max Event Validity Delay | Allows events to have a range of time that they are valid. This value works with the Processing Delay to define a time range. | 
| Message Library Path | Defines the org_unit object for a Patron Message Center message. | 
| Message Template | A Template Toolkit template that can be used to generate output for a Patron Message Center message. The output may or may not be used by the reactor or another external process. | 
| Message Title | The title that will display on a Patron Message Center message. | 
| Message User Path | Defines the user object for a Patron Message Center message. | 
| Opt-In Settings Type | Choose which User Setting Type will decide if this event will be valid for a certain user. Use this to allow users to Opt-In or Opt-Out of certain events. | 
| Opt-In User Field | Set to the name of the field in the selected hook’s core type that will link the core type to the actor.usr table. | 
| Success Cleanup | After an event is reacted to successfully a cleanup module can be run to clean up after the event. | 
| Template | A Template Toolkit template that can be used to generate output. The output may or may not be used by the reactor or another external process. |