Explain what a session save handler proxy is

[chrisyue]

https://github.com/symfony/symfony-docs/blob/master/components/http_foundation/session_configuration.rst#save-handler-proxy

why not tell readers about what a proxy is, what it used for, or why we should know about these stuff.

and the section session lifetime and session cookie lifetime is telling us a same thing isn't it?

and in the section Native PHP Save Handlers mentions that:

Specific details can be found in docblock of the setOptions() method of each class.

which class? handler class? I don't see a setOption() method in any of those handler class

[cordoval]

answer to the session lifetime is yes they are the same

about the setOption thing i am submitting a PR

and about the what is a proxy question see the PR too,

i think this chapter is one of the best written chapters ever by @Drak, I am amazed you have these questions but in any case here is a PR to clarify even further

[wouterj]

Seems to be fixed by #3423