Skipping Over Fields
A Skip expression can conditionally make a field read-only. If the expression evaluates to TRUE (.T.), the field is skipped; otherwise, it is not. For example, if you have a table that contains both billing address fields and shipping address fields for customers, you can use a Skip expression to skip the shipping address fields if the first line of the shipping address field reads "Same." You might want to make a field conditional based on who is logged on.
iff(user_name()= "Fred", .F., .T.)
You may want to always skip some fields. Field values set by Field Rules ( Calculated, Auto-Increment, Default, and Lookup) are often skipped, so the user does not change them. To always skip a field, specify a Skip expression that is always TRUE (e.g., .T.).
In the Control Panel select the table and click Table > Edit Field Rules.
Display the Data Entry tab.
Enter an expression in the Skip field. The condition must evaluate to TRUE (.T.) or FALSE (.F.). Click 'xy' to use the Expression Builder to help you define the expression.