I my customer project i need this function for the following scenario. The user has to choose a value from dropdown list. If the selected item from dropdown has a special value, the user should get a message, that informs him about a special situation and that he should confirm to proceed.
After that the message appears if you click the save button:
Hope this helps you.
I already posted about SharePoint forms or Listforms. Let me give you the links to my previous posts: