$ERR <Text>$ERROR <Text>
The $ERROR command outputs an error message to the screen in a message box,
and it behaves as a syntax error during the input phase of the timetable files:
the timetable won't run.
This command is mostly used at checking the options, which were set by the user.
The options are defined by the $OPTION command,
Traffic shows them in the Option menu of the Configuration window,
allowing the user to check or uncheck the menu items.
If the timetable file cannot run getting conflicting option values,
you can show an error message for the user, and to prevent the timetable file to run.