An empty <?php?> Codeblock in PHP 7.2.0 will put out an "Unquoted strings" warning. To prevent that, add at least one empty space into the codeblock.
Example:
<?php
<?php/*
echo "This was some useful code.\n";
*/?>
?>
Gives: PHP Warning: Use of undefined constant php - assumed 'php' (this will throw an Error in a future version of PHP)
Fix via:
<?php
<?php /*
echo "This was some useful code.\";
*/?>
?>
Don't know if that is an intentional behaviour or a side effect.