Priority mandatory in customer portal

[vinesh]

can some one help me on Priority mandatory in customer portal, i have tried below in CustomerTicketMessage.dtl but no success, please let me know where and how can i make Priority mandatory in customer portal

<!-- dtl:block:Priority -->
<div>
<label class="Mandatory" for="PriorityID"><span class="Marker">*</span>$Text{"Priority"}:</label>
$Data{"PriorityStrg"}
<div id="PriorityError" class="TooltipErrorMessage"><p>$Text{"This field is required."}</p></div>
<!-- dtl:block:Priority -->