/*!
# `TRON | TROFF`
## Purpose
Enable and disable trace printing.
## Remarks
When tracing is on, the executing line number will be printed
as the program is running.
## Example
```text
10 FOR I = 1 TO 3
20 TROFF:IF I = 2 THEN TRON
30 PRINT I
40 NEXT I
RUN
1
[30] 2
[40][20] 3
```
*/