<?php

$myhtml = '<html>
<body>foo bar
<?php echo "hello world"; ?>
baz
</body>
</html>';

function strip_php($text) {
	$tokens = token_get_all($text);
	foreach($tokens as $index => $token) {
		if(!is_array($token) || token_name($token[0]) !== 'T_INLINE_HTML') {
			unset($tokens[$index]);
		}
		else {
			echo $token[1];
		}
	}
}

strip_php($myhtml);