How does is_member_of() work?

[James Birkett]

How does the is_member_of function work?

I can't seem to get this code to work:

PHP Code:

if($vbulletin->options['username_manipulation_userid']){
    $array = explode(';', $vbulletin->options['username_manipulation_userid']);
    $exempt = $vbulletin->options['username_manipulation_shuffle_exempt'];
    foreach($array as $usid){
        if((!is_member_of($vbulletin->userinfo, $exempt)) && ($user['userid'] == $usid)){
            // execute code here (i know this works)
        }
    }
} 


It doesn't seem to recognize my exceptions, but executes the code anyway.

I would take a guess that the is_member_of() doesn't take userid parameters..
Thanks in advance.