londrum - 8:09 pm on Sep 15, 2012 (gmt 0)
it's possible to set (or overwrite) a GET variable or a POST variable in your script, just be writing
$_GET['page'] = 'blah';
$_POST['page'] = 'blah';
so they don't have to come from a URL or a form (although they usually do).
i think isset just checks whether a variable exists. it doesn't care where it came from.