Pop up warning message

Hi,

Can we display warning message in Adobe campaign classic through input form? if yes then how? Please suggest.

Since don't know how to display warning message in input form I tried for error message.

I have written below code in nms:delivery input form-

<if expr="EV(@messageType, 'sms')">
<check expr="[../content/sms/source] !='' ">
<error>"Sure? you not added consumer number."</error>
</check>
</if>

The above code is working fine when I open sms delivery template and when click on save its showing error message if text content is not empty. But when I tried below code its not showing any error message even when text content is not equal to ABC:

<if expr="EV(@messageType, 'sms')">
<check expr="[../content/sms/source] !=''ABC">
<error>"Sure? you not added consumer number."</error>
</check>
</if>

Please guide here.