Extensions include the period. For example:
spl_autoload_extensions(".inc, .php, .lib, .lib.php ");
(PHP 5 >= 5.1.2)
spl_autoload_extensions — Register and return default file extensions for spl_autoload
When calling without an argument, it simply returns the current list of extensions each separated by comma. To modify the list of file extensions, simply invoke the functions with the new list of file extensions to use in a single string with each extensions separated by comma.
A comma delimited list of default file extensions for spl_autoload().
A quick note for anyone using this function to add their own autoload extensions. I found that if I included a space in between the different extensions (i.e. '.php, .class.php') the function would not work. To get it to work I had to remove the spaces between the extensions (ie. '.php,.class.php'). This was tested in PHP 5.3.3 on Windows and I'm using spl_autoload_register() without adding any custom autoload functions.
Hope that helps somebody.