I've to make come check on the newform and editform in custom list. I've to check if a field has a value if an other has. I've to check if a document depending on meta already exist in an other library. If it's true i've to alert the user and ask if we replace it or not. If not we return to the form.
Maybe can i use event receiver in itemupdating and cancel but how to return to the form and display message?
how can i achieve this type of operation?