The primary page passed to Trigger activities is the top-level page corresponding to the Applies To class of the rule.
An activity of type Trigger may alter properties, call functions and execute other rules, but do not perform database commits. Take care in declarative processing not to specify processing that produces infinite looping.
When you choose In Background on Copy in the Execute field, the triggered activity runs in a child requestor in parallel to the current requestor. This means that:
During execution of a Declare Trigger rule, the page on which the rule operates temporarily becomes the primary page. The page keyword PRIMARY and the results of the tools.getPrimaryPage() PublicAPI method reflect this change.
When the Declare Trigger rule execution completes, the primary page of the calling activity resumes as primary.
Using the Tracer, you can watch the evaluation of a Declare Trigger rule if the Execute field value is Immediate:
Declare Trigger rules can automatically update the history of a work item, rule, or data object when certain properties change.
For work item change tracking, use the Field Auditing gadget, on the Work History landing page.
For data or rule tracking, see PDN article How to audit field-level changes to security rule and data instances.
Click Actions > View Java to view the generated Java of a rule. You can use the Java code to debug your application or to examine how rules are implemented.