Is there a parameter or some variable/array/something you can set from a callback_before/after_insert/update where you can set a custom error message?
You have an article form... and you include some custom field. You check that its value it's ok with the function callback_before_insert/update. If it's not you just return false. Is there (already) a way to set the error message so you can tell the user WHY it failed?
Thanks in advance!