Online editor should alert about unsaved changes
When I edit a worksheet online and accidentally click on the Cancel button in the lower right corner, the editor discards all unsaved work without warning. It should really alert a user about any unsaved changes.
I keep loosing hours of work because of this simple missing feature as I tend to accidentally click on Cancel button whenever I want to close some menu inside the cluttered editor window.
I'd also suggest to rename the button from "Cancel" to "Cancel Editing".