Which backslash escape will be the last to get meaning in perl?

• \F (Update 2015-06-08: \F is now used starting from perl 5.16.0)
• \I
• \J
• \M
• \O
• \P (Update 08 aug 29: \P is used up, dunno how I messed this up.)
• \T
• \Y
• \i
• \j
• \m
• \o (Update 2010-11-24: remove: \o is now used starting from perl 5.13.3)
• \q
• \y
• some punctuation
• some control char
• some non-ascii
• another double meaning
• (Update:) third meaning for \1 or \b or \N (Update 2010-11-24: added \N for it too now has two meanings)

Don't worry, vim regexen are much worse.