How to manage attachment relationships for specific posts in WP 3.5+

In WordPress 3.5, media management has changed entirely. Also, relating attachments to specific posts is (I believe) basically only being done for backward compatibility. Therefore, after uploading attachments from within the media modal to a post of any post type, it establishes a relationship where the post ID is the parent of the attachment ID, like it’s been for a long time.

How to create a theme customizer ‘sub’ panel?

One of the cool new features of WordPress 4.0 is the add_panel() method. In my situation, i’d like to create a new panel for theme options, that’s very straight forward, but is it possible to create sub panels under the them options panel, for example one for the header, one for body and one for the footer? If so, how would I go about doing it?