I'm working with media 7.x-2.0-unstable7.
I am attempting to adjust the behavior of the media module's wysiwyg embedded image attribute editor modal dialog (c.f. http://drupal.org/node/835516). It was pretty easy to adjust the contents of this dialog with hook_media_format_form_prepare_alter (see: http://drupal.org/node/835516#comment-7075374), and I expected that it would be easy to add a submit handler, and Drupal would jump through the hoops for me to insure that it was called at the right time. If this service is offered, I can't seem to figure out how to make it work.
media.api.php did not help clarify.