title: CodeIgniter - best place to declare global variable
body: <p>I just want to use a <code>$variable</code> at several places: not only views and controllers, but also in the <code>routes.php</code> and other configuration files.</p>
  
  <p>I don't want things like: use the Config class to load configuration files; use CI's <code>get_instance</code>, et cetera.</p>
  
  <p>I just want to declare a given <code>$variable</code> (it could be a constant, but I need it as a variable), and use it absolutely everywhere.</p>
  
  <p>In fact... I'd like to know which PHP file in the CI bootstrap is one of the first to be parsed, so I could introduce my global variable there... but not a core/system or inapproriated file, but the "best" suited placement for this simple requirement.</p>