Progression through fields on the form is orderly. The current record is displayed on the form until you explicitly choose to go to another record. The form is attractive and easy to read. You can be sure that all the data entered in a field follows a specified format by defining an input mask. The input mask defined for the CustomerID text box on the Customers form ensures that values entered are five uppercase letters.
Access displays blanks as a guide.
If the data you enter doesn't match the mask, Microsoft Access displays an error message. Note The InputMask property for CustomerID was set at the table level. When the CustomerID text box was created on the Customers form, it inherited the setting for the InputMask property from the Customers table. If you want users to know that they've entered an incorrect value when they attempt to leave a control, you can use a macro or event procedure in the control's BeforeUpdate property. The macro used in the Customers form uses the DLookup function to verify a value that you type in the CustomerID text box against the values that already exist in the table.