<?php

// Using !!! as a placeholder
$code = "<script>alert(foo <!!! bar);</script>";

for ($char = 33; $char <= 126; $char++)
{
    $c = chr($char);
    $new_code = str_replace('!!!', $c, $code);
    echo "'$new_code' => '" . strip_tags($new_code, '<script>') . "'" . PHP_EOL;
}

?>