Drupal 7: Rendering system

How does Drupal render 'render elements':

$account->content['example'] = array( {renderable array information on the t('Content')} ); (#1)

$account->content['example']['output'] = array( {renderable array information on the $content} ) (#2)

Where does drupal pass render elements to 'drupal_render()'?

Below is the entire hook function that contains the two render elements (#1), and (#2).

- - -

function example_user_view($account, $build_mode) {
  if (!user_access('view content creation permissions')) {
    return;
  }

  $node_types = node_permissions_get_configured_types();
  if (empty($node_types) {
    return;
  }

  $list = array();
  foreach ($node_types as $type) {
    if (user_access('create' . $type . ' content', $account)) {
      $list[] = check_plain(node_type_get_name($type));
    }
  }

  if (!empty($list)) {
    $variables = array (
      'items' => $list,
    );
  }
  $content = theme('item_list', $variables);
  if (!isset($account->content['example'])) {
    $account->content['example'] = array();
  }
  $account->content['example'] += array (
    '#type' => 'user_profile_category',
    '#attributes' => array('class' => array('user-member')),
    '#weight' => 5,
    '#title' => t('Content'),
  );
  $account->content['example']['output'] = array (
    '#type' => 'user_profile_item',
    '#title' => t('Content creation permissions'),
    '#markup' => $content,
    '#attributes' => array('class' => array('content-creation')),
  );
}