PHP strrpos()

<?php
strrpos($string,$find)
?>

<?php
$mystring = "wxyz";
$pos = strrpos($mystring, "b");
if ($pos === false) { 
    echo "not found<br>";
}
$mystring = "abcdef";
$pos = strrpos($mystring, "b");
if (is_bool($pos) && !$pos) {
    echo "not found<br>";
}
?>