Programmatic Elements - Beginning Oracle Application Express 4.2 - page 261

Figure 8-7. Specifying the sequence, name, and display location

7. Select Not Null for the validation type from the options shown in Figure

8-8 .

Figure 8-8. Selecting a validation type

8. In the validation step of the wizard, enter a custom error message. The error

message in Figure 8-9 uses a substitution variable #LABEL# to include the
label of the item in the message. This way, when the label on the form item
changes in the future, the validation error message will automatically refer-
ence the new label.