<DataSource ID="regularExpression">
    <fields>
        <field name="email" title="Email" type="text">
            <validators>
                <validator type="regexp" 
                           expression="^([a-zA-Z0-9_.\-+])+@(([a-zA-Z0-9\-])+\.)+[a-zA-Z0-9]{2,4}$"/>
            </validators>
        </field>
    </fields>
</DataSource>
