Uninstall Cancel Confirm

I am using the MUI with MUI_ABORTWARNING. My installer will prompt for confirmation on a "Cancel" but my uninstaller, created by the install, will not. I tried to use the un.onUserAbort function but it says that it's already defined. What can I do to make the uninstaller confirm on a "Cancel"? Mostly I want to detect the cancel so I can clean up some files from the uninstaller.

For uninstaller it is MUI_UNABORTWARNING

Thanks!

I found the additional information to catch the user abort to clean up the files.

!define MUI_CUSTOMFUNCTION_UNABORT un.userAbort

Function un.userAbort
;do stuff
FunctionEnd

The problem I was having with the user manual was that the instructions for the "Modern User Interface" mode was different from all of the other instructions.