PHP session_destroy and session scope?
===

OK there are many "simple session" questions out there, but I can't seem to find what I'm after. It bugs me a little bit as the PHP document does not seem to explain this well.

Three fold questions.

1. It says that session_destroy() wipes out the session data but not the global variable. So it wipes the data but the variables are still in tact? What does the documentation mean by global variables?

2. What are the different types of ways that I can use to destroy session data, isn't session_destroy enough? Why would you use the below coding as I've seen in some code examples:

    session_start();
    $_SESSION = array();
    session_destroy();

3. Session seem to persist across browser instances. For example, IE9 will keep the same session id when two separate browsers are opened. Same with Chrome. Only when I close all the browsers, will I get a new session id. Is this always the case for all browsers? I want to know so that I can keep this in mind during my coding - wouldn't want to find out later that some browsers are not persistent and my code thinks that it does, then run the risk of producing all sorts of errors.

Thanks in advance for anyone who can help me answer these questions.