I am currently working on developing custom post types in WP 3.0 (custom meta boxes, custom fields, etc). In some cases on a save_post hook I am doing some back-end verification (like, to see if an uploaded image fits the required dimensions or a custom caption length does not exceed XX characters).
In case the verification fails, I would like to display users notifications (around the place where the "Post updated" message appears). However I can't find anything about how that could be done. I definitely know that some plugins throw such notifications on their own pages, but browsing through their code did not help.
Any guidance would be appreciated ;)