How to display web-users of a current web-group

<?php
// ShowUserList - MODx snippet to display the users assigned to a given web group.
// the webgroup is set in the snippet properties tab or the snippet call.
// &webgroup=webgroup;text;webgroupname
// [[ShowUserList? &webgroup=`webgroupname`]]

// check for valid web user group
if(!isset($webgroup) || $webgroup == '') { return; } // quietly do nothing if webgroup is not set
$result = $modx->db->select('id',$modx->getFullTableName('webgroup_names'),"name = '".$webgroup."'");
if($modx->db->getRecordCount($result) != 1) { return; } // quietly do nothing if webgroup does not exist

$table1 = $modx->getFullTableName('web_users');
$table2 = $modx->getFullTableName('webgroup_names');
$table3 = $modx->getFullTableName('web_groups');
$results = $modx->db->select("tbl1.username", "$table1 AS tbl1, $table2 AS tbl2, $table3 AS tbl3", "tbl2.name='$webgroup' AND tbl3.webgroup=tbl2.id AND tbl1.id = tbl3.webuser", 'tbl1.username ASC');
$userlist = '';
while($users = $modx->db->getRow($results)) {
  $userlist .= $users['username'].'<br />';
}

return $userlist;
?>

<?php
echo "<pre>";
print_r($_SESSION);
echo "</pre>";

<?php
/*  [!webgroup_names!]

*/
$webgroups ='';
if(isset($_SESSION['webUserGroupNames'])){
   $count = count($_SESSION['webUserGroupNames']);
   if($count > 0){
      $webgroups .='<ul>';
      foreach($_SESSION['webUserGroupNames'] as $wugn){
        $webgroups .='<li>'.$wugn.'</li>';
      }
      $webgroups .='</ul>';
   }
}

return $webgroups;
?>