PHP Manual: Default implementation for _

Description

void spl_autoload ( string $class_name [, string $file_extensions = spl_autoload_extensions() ] )

This function is intended to be used as a default implementation for __autoload. If nothing else is specified and spl_autoload_register is called without any parameters then this function will be used for any later call to __autoload.

Parameters

class_name: The lowercased name of the class (and namespace) being instantiated.
file_extensions: By default it checks all include paths to contain filenames built up by the lowercase class name appended by the filename extensions .inc and .php.

Return Values

No value is returned.