To perform a script while entering a field you can connect the script
directly with the field. Removing the field from tab order prevents it from
beeing entered other then by mouse click.

To perform a script while leaving a field you might try to catch the user in
a loop. Unfortunately this is very embarrassing for the user because he
doesn't understand what is going on.

Alternatives are PlugIns, which start scripts when field values are changed.

Jens

I found a simple method.

Clicking on the field triggers a script that Pauses. It waits for you to
enter data in the field, then when you hit enter, Resumes the script. The
rest of the script includes an evaluation of the target field, and branches
based on contents.

As long as your user hits Enter after filling in the field it works, so you
might need to use a popup or put an Enter button on the layout as a
reminder.

HTH