Some variables passed to built-in (and custom) functions are set by the function (output parameters) and don't need to be initialized before the call. A prime example is preg_match:

    if (preg_match('/foo/', 'the foobar', $matches) { ... }

Here, any value given to $matches before the call will be overwritten by the call itself, i.e., the call is guaranteed to initialize the variable.

IDEA

Since there's no way to declare this in PHP, use a simple inline comment in the NetBeans-supplied header files and make this available to custom code as well:

    function preg_match (
        $pattern, $subject, /* out */ array &$matches = null, $flags = 0, $offset = 0
    ) {}