2.10.8.2 Trace Points

Trace points are a separate feature from trace mode that allow writing specified ports to the console when a predicate is being evaluated. It does not ever pause program execution and does not need to be in trace or debug mode to work.

They are turned on via trace/1 and trace/2.

They don't pay attention to visible/1 (because the ports shown are set in trace/2) or leash/1 (because they don't pause execution).

They can be turned off via trace/2.