I am trying to add some metaboxes to post edit page. They contain essential data for my template so I have to make sure they are filled and valid.
Validating them is not a problem. Before saving data I check them. But what to do when they are incorrect? I would like to stop saving process and print some nice error message but I have not found any reasonable way to do that. The post shall not be saved without these forms validly filled.
Thanks for help.