Description:
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 It is not clear from the PHP5 class documentation how important the order of class definition is in the the context of multiple levels of inheritance.

 According to the PHP4 doc on extends @ http://php.net/manual/en/keyword.extends.php the following code is incorrect due to the order in which the classes are defined:

class one extends two {}
class two extends three {}
class three {}

However PHP5's docs make no mention if the order of definition is still significant. OR if its only significant when there are multiple levels of inheritance. The preceding code throws a fatal error 'class not found' for the class two.  

The following code however does work:
class one extends two {}
class two {}

Request clarification please.