Note: 
      In PHP 4.0.1pl2, three extra classes are returned at the beginning of
      the array: stdClass (defined in 
      Zend/zend.c),
      OverloadedTestClass (defined in
      ext/standard/basic_functions.c) 
      and Directory
      (defined in ext/standard/dir.c).
     
      Also note that depending on what libraries you have compiled
      into PHP, additional classes could be present. This means that
      you will not be able to define your own classes using these
      names. There is a list of predefined classes in the Predefined Classes section of
      the appendices.