Validators are Boolean expressions that ensure that the variables that may be modified via a client view satisfy certain constraints. For example, they can ensure that values stay within a predefined range or that certain variable values have been entered at all. If a validator expression evaluates to "false", a message is presented to the user who performed the task, so that the error condition may be resolved by continuing work on the task.

Validators can be specified to verify each "save" of variables. When defining the validator, set validatedOnSave="true". In this case, you will get an error message if you try to save and the validator expression evaluates to "false".