PHP opening and closing recommended tags?

PHP opening and closing recommended tags?

 The three different forms are as follows:

1. <?php
   echo “this is the recommended style”;
   ?>
2. <script language="php">
   echo “this style is also available”;
   </script>
3. <?
   echo “this is short tags style; it needs to be configured”;
   ?>

There is also another form which may or may not be supported on some browsers. It is shown as below:
 <%
echo ‘this is ASP-style tags; it may not be available';
 %>