<com:TForm ID="form1">
	<h1>Callback Enabled Calculator</h1>
	
	<com:TActiveTextBox id="a" />
	+
	<com:TActiveTextBox id="b" />
	=
	<com:TActiveTextBox id="c" />
	
	<com:TActiveButton id="sum" 
		onclick="do_sum" 
		text="Calculate!" />
	
	<com:TRequiredFieldValidator 
			ControlToValidate="a"
			ErrorMessage="left summand is required."
			ControlCssClass="required"
			Display="None" />
	<com:TRequiredFieldValidator
			ControlToValidate="b"
			ErrorMessage="right summand is requied."
			ControlCssClass="required"
			Display="None" />

	<div class="summarybox">
		<com:TValidationSummary
			ID="summary"
			HeaderText="Unable to calculate because" />
	</div>
	
</com:TForm>