PHP friend/package visibility

Until today there's no language construct to limit the visibility. But you can annotate your class with phpDocumentor's @internal:

The @internal tag can be used as counterpart of the @api tag, indicating that the associated Structural Elements are used purely for the internal workings of this piece of software.

It's up to the API user to follow that suggestion.

As stated here:

No. You can set a variable after declaring a namespace, but variables will always exist in the global scope. They are never bound to namespaces. You can deduce that from the absence of any name resolution descriptions in http://www.php.net/manual/en/language.namespaces.faq.php