@lupo49: ahh, got it. thanks for the explanation. The reason why I wanna do it: I have a group with only rights to a single namespace within the wiki. If they connect to the wiki without the full namespace addressed in the url they don't see anything and aren't able to navigate at all.
Setting is for namespace projekte:dnb-test:* and group: reading. This group has no further rights in any area of the wiki.
@turnermm: Thanks for the mentioning of $_REQUEST. Took me a bit try and error but got it working now with this code after
$SUM = $_REQUEST['summary']; around row 40 in doku.php:
if ($_REQUEST['u'] && (strtolower($_REQUEST['u']) == 'jana'))
$ID = 'projekte:dnb-test:0start';
:)
Thank you very much!