Configurable persistent session key?

[sodabrew]

In #344 there is a request to bring back the configurable PERSISTENT in the session save_path. I'm not sure I follow the reason for configuring this if it's just an opaque token used to stash the connection handle into the PHP global EG(persistent_list) hash.

In php-memcached 2.x, the session key was set by taking the characters following PERSISTENT= and affixing them after memcached_sessions:id=.

In php-memcached 3.0, the session key was set by taking the entire save_path and affixing it after memc-session:.

It seems reasonable to make this configurable in the INI file, but I don't understand the use case for knowing the key. https://devzone.zend.com/446/extension-writing-part-iii-resources/