Using old code with new versions of PHP
   
    Now that PHP has grown to be a popular scripting language, there are
    a lot of public repositories and libraries containing code you can reuse.
    The PHP developers have largely tried to preserve backwards compatibility, 
    so a script written for an older version will run (ideally) without changes
    in a newer version of PHP. In practice, some changes will usually be needed.
   
   
    Two of the most important recent changes that affect old code are:
    
     - 
      
       The old $HTTP_*_VARS arrays are not available as of 
       PHP 5.4.0. The following 
       superglobal arrays
       were introduced in PHP » 4.1.0. 
       They are: $_GET, $_POST, 
       $_COOKIE, $_SERVER, 
       $_FILES, $_ENV,
       $_REQUEST, and $_SESSION.  
      
     
- 
      
       External variables are no longer registered in the global scope by
       default.  In other words, as of PHP
       » 4.2.0 the PHP directive 
       register_globals is 
       off by default in php.ini. The preferred 
       method of accessing these values is via the superglobal arrays mentioned
       above.  Older scripts, books, and tutorials may rely on this 
       directive being on.  If it were on,
       for example, one could use  $id from the URL 
       http://www.example.com/foo.php?id=42.  Whether on 
       or off, $_GET['id'] is available.
      
     
    For more details on these changes, see the section on 
    
predefined variables
    and links therein.