Custom validation conditions may be applied to any validation widget through the validIf and missingIf attributes. The validIf attribute applies a custom validation condition to the widget:

<dsp:tagAttribute name="validIf" value="this.getValue() != 'blank'"/>

In the above example, the widget will be considered valid only when the expression in the validIf attribute evaluates to true.

The missingIf attribute applies a custom condition to determine whether the widget is missing a required value.