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

To have VA Smalltalk check for errors keystroke-by-keystroke, set thenotifyChangeOnEachKeystroke property to true in the part's settings. Otherwise, set the reformatOnFocusChange property to true to validate the data after the user finishes entering data and moves on to a different part.

When an error is detected, VA Smalltalk displays an error message (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.