title: What exactly is the PHP function session_module_name for?
body: <p>PHP Session related functions have this one: <a href="http://www.php.net/manual/en/function.session-module-name.php" rel="nofollow noreferrer">session_module_name</a>. The documentation only says: </p>
  
  <blockquote>
    <p>session_module_name — Get and/or set the current session module</p>
  </blockquote>
  
  <p>Nothing about what session modules are, what options available, and when it to use. </p>
  
  <p>What is the purpose of this function?</p>