Panels 3 API

Can anyone let me know if there's a panels API documentation available online. Would like to have a quick overview, but couldn't find it on api.drupal.org.

I have a problem with apache_solr + panels. When making a layout with left an right region. Left = facets (key = left), right = search results (key = right). The problem is that the facets aren't shown, because the search result aren't available when rendering the facets. First the right region should be rendered, then the left version.
Any idea how and with which hook I would be able to sort the render order.

Thanks!