Also, the double underscore prefix is reserved for magic methods:

    PHP reserves all function names starting with __ as magical. It is
    recommended that you do not use function names with __ in PHP unless you
    want some documented magic functionality.

It's only explicitly reserved for functions, so you're technically ok here, but it still may cause confusion.

http://www.php.net/manual/en/language.oop5.magic.php