Note: 
    In PHP 3, objects will lose their class association
    throughout the process of serialization and unserialization. 
    The resulting variable is of type object, but has no class
    and no methods, thus it is pretty useless (it has become
    just like an array with a funny syntax).
   
| Caution | 
| 
    The following information is valid for PHP 4 only. 
    | 
   serialize() returns a string containing a
   byte-stream representation of any value that can be stored in
   PHP. unserialize() can use this string to
   recreate the original variable values. Using serialize to
   save an object will save all variables in an object.  The
   functions in an object will not be saved, only the name of
   the class.
  
   In order to be able to unserialize() an object, the
   class of that object needs to be defined. That is, if you have an object
   $a of class A on page1.php and serialize this, you'll
   get a string that refers to class A and contains all values of variabled
   contained in $a. If you want to be able to unserialize
   this on page2.php, recreating $a of class A, the
   definition of class A must be present in page2.php. This can be done for
   example by storing the class definition of class A in an include file and
   including this file in both page1.php and page2.php.
  
   If you are using sessions and use session_register()
   to register objects, these objects are serialized automatically
   at the end of each PHP page, and are unserialized automatically on
   each of the following pages. This basically means that these objects
   can show up on any of your pages once they become part of your
   session.
  
   It is strongly recommended that you include the class
   definitions of all such registered objects on all of your
   pages, even if you do not actually use these classes on all
   of your pages. If you don't and an object is being
   unserialized without its class definition being present, it
   will lose its class association and become an object of class
   stdClass without any functions available
   at all, that is, it will become quite useless.
  
   So if in the example above $a became part of a session
   by running session_register("a"), you should include the
   file classa.inc on all of your pages, not only page1.php
   and page2.php.