The validation element is used to validate answers on a question page. Each validation element has an expression, which is used to evaluate if an answer is a valid answer. The expression must evaluate to true for the script execution to proceed beyond the page containing the validation element. For example, the following validation element displays a warning message if the value for the wage amount is less than or equal to zero:
<validation expression="Income.wageAmount > 0 "> <message id="Page2.noWageValidationMessage"> <![CDATA[You entered %1d as your wage amount. Please enter a value greater than zero.]]> <argument id="Income.wageAmount" /> </message> </validation>