Apache/1.3.14 (Unix) PHP/4.0.3pl1
# "If both track_vars and register_globals are enabled, then the globals variables and the $HTTP_SESSION_VARS entries will reference the same value." - PHP Manual.
# In the next example $HTTP_SESSION_VARS[xyzzy] can only be read, if it's written, the new value is lost, it doesn't get saved through requests.
# Besides that, setting $xyzzy to something isn't reflected in its $HTTP_SESSION_VARS counterpart until the next request.

session_register("xyzzy");
$HTTP_SESSION_VARS[xyzzy] = 'nothing';
$xyzzy = 'something';
# Here, $HTTP_SESSION_VARS[xyzzy] is equal to 'nothing'.
$HTTP_SESSION_VARS[xyzzy] = 'somethingelse';
# Here, $HTTP_SESSION_VARS[xyzzy] is equal to 'somethingelse'.

# At the next request, $HTTP_SESSION_VARS[xyzzy] will be equal to 'something'.