When the user enters data into a field, the field is checked for errors either after the field loses focus, or on a keystroke-by-keystroke basis as the user types.

To have errors for non-numeric fields checked keystroke by keystroke, select Signal events on each keystroke on the Settings view of the part. Otherwise, select Reformat on focus change to validate the data after the user finishes entering data and selects a different part.

If you do not select either of these options, the field is still validated, but you will need to handle the error yourself. Usually when an error is detected, an error message is displayed (such as *error*) in place of the incorrect value. When the user clicks on or tabs to the field to correct the error, the original value is displayed again, so it can easily be corrected.

You can use the Form Input Checker part to assist you in checking for errors.