How to reproduce

• Connect to cms
• edit a content
• add a file field
• set a rule extension to ".jpg"
• Save
• fill the form with a picture "test.JPG"
• submit

Actual behavior

• A message is displayed in a new window that the file has not a valid extension
• no tooltip to help the contributor to define the extension, how to set more than one? should I set .jpg or only jpg...?

Expected behavior

• a pop-up instead of a new page
• a tooltip to explain how to set this field
• no case sensitive