1.  <?php echo 'if you want to serve PHP code in XHTML or XML documents,
                use these tags'; ?>
2.  You can use the short echo tag to <?= 'print this string' ?>.
    It's equivalent to <?php echo 'print this string' ?>.
3.  <? echo 'this code is within short tags, but will only work '.
            'if short_open_tag is enabled'; ?>