Developing PHP5 code on a PHP4 server, that also has PHP5

.htaccess to run PHP5 on a server that defaults .php to PHP4, when your ultimate target is a PHP5 server.

.htaccess file

RewriteEngine   On
RewriteRule   ^index.php5$      - [L]
RewriteRule   ^exec.php$        - [L]
RewriteRule   ^(.*)\.php5?$     index.php5?page=$1
DirectoryIndex  index.php5

The advantage of this architecture is that since all the pages are delivered through index.php5, they are processed as PHP5, although they are named as .php.

Also - if you have a PHP5 application, you MAY be able to use the same approach, if you put PHP5 and PHP4 on the same server.