Something

<?php 
	session_start();

	if(isset($_SESSION['username'])) {
		header("Content-type:text/xml;charset=utf-8");
		print '<?xml-stylesheet type='text/xsl' href='calendar.xsl'?>';
		?>
		<calendar>
			<date>
				<year><?php echo date('Y'); ?></year>
				<month><?php echo date('m'); ?></month>
				
			</date>

			<bookings>
				<booking>
					<id>13</id>
				</booking>
				<booking>
					<id>12</id>
				</booking>
				<booking>
					<id>14</id>
				</booking>
			</bookings>
		</calendar>
		
<? } 
	else {
		echo 'not logged in';
	}

?>