- With the setting TraceOn->patt, Trace and related functions do not start tracing until they encounter expressions to evaluate which match the pattern patt. This pattern is also tested against tags associated with the evaluation.
- TraceOff can be used within tracing switched on by TraceOn.
- Once tracing has been switched off by TraceOff, however, TraceOn will not switch it on again.
- During the execution of Trace, the settings for TraceOn and TraceOff can be modified by resetting the values of the global variables and .
Introduced in 1991