PHP Catchable fatal error: Argument 1 passed to foo() must be an instance of string, string given, called in..

"foo" == TRUE, and "foo" == 0… but, of course, TRUE != 0

Incrementing (++) a NULL produces 1. Decrementing (--) a NULL produces NULL. Decrementing a string likewise leaves it unchanged.

et ça c'est très bon:

When you use AddHandler, you are telling Apache that “execute this as php” is one possible way to handle .php files. But! Apache doesn’t have the same idea of file extensions that every human being on the planet does. It’s designed to support, say, index.html.en being recognized as both English and HTML. To Apache, a file can have any number of file extensions simultaneously.
Imagine you have a file upload form that dumps files into some public directory. To make sure nobody uploads PHP files, you just check that they don’t have a .php extension. All an attacker has to do is upload a file named foo.php.txt; your uploader won’t see a problem, but Apache will recognize it as PHP, and it will happily execute.