Multi-Select Listbox

<?php
/**
 * Supports listing out the contents of a single folder that can contain pages or 
 * folders up to 2 levels deep only, e.g. if you have a folder of pages (one page
 * for one "category") :
 *
 * Categories
 *          +--- SubCategory1
 *          |       +--- EndCategory1
 *          |       +--- EndCategory2
 *          |
 *          +--- SubCategory2   
 *          +--- SubCategory3   
 */
  
// Get top-level categories
 
$criteria = array();
$criteria['parent'] = (int) $parent;
$criteria['deleted'] = '0';
$criteria['published'] = '1';
$criteria['hidemenu'] = '0';
 
 
$query = $modx->newQuery('modResource', $criteria);
 
$resources = $modx->getCollection('modResource', $query);
 
$output = array();
 
$top_level_ids = array();
foreach ($resources as $r) {
    $output[] = $r->get('pagetitle') .'=='.$r->get('id');
    // Get sub-levels
    if ($r->get('isfolder')) {
        $criteria['parent'] = $r->get('id');
        $query = $modx->newQuery('modResource', $criteria);
        $sub_resources = $modx->getCollection('modResource', $query);
        foreach ($sub_resources as $sr) {
            $output[] = ' ---- '.$sr->get('pagetitle').'=='.$sr->get('id');   
        }
    }
}
 
return implode('||',$output);