Escaping from HTML

There are three ways of escaping from HTML and entering "PHP code mode":

Example 5-1. Ways of escaping from HTML 1. <? echo("this is the simplest, an SGML processing instruction\n"); ?> 2. <?php echo("if you want to serve XML documents, do like this\n"); ?> 3. <script language="php"> echo("some editors (like FrontPage) don't like processing instructions"); </script>