What are Panes, in a Übercart context? I was wondering what are "Panes" - I found them while I was messing with source code of Ubercart module. It looks like they're building page with something like panes - which I'm totally new to. Code looks like:

  // Load through the cart panes...
  foreach (uc_cart_cart_pane_list($items) as $id =&gt; $pane) {
    // If the pane is enabled...
    if ($pane['enabled']) {
      // Add its output to the cart view.
      $build[$id] = $pane['body'];
      ...


So, are "panes" Ubercart concept, or some in-general thing? I searched with "Drupal Panes" but no luck.
Visit your checkout page (add product to cart, visit cart, then click Checkout), each fieldset (as in image) is a pane. It's not the same as for "panels" pane.