The answer is at
:help :map-<special> (or
:help :map-special, which is easier to type):
Define a mapping with <> notation for special keys, even though the "<" flag
may appear in 'cpoptions'. This is useful if the side effect of setting
'cpoptions' is not desired. Example: >
:map <special> <F12> /Header<CR>
Some values for
cpoptions will not allow
<> notation for keys, meaning they have to be entered literally (like the old vi days); e.g., you would put
map - /Header^M
^M is actually a single byte inserted with Ctrl-V Enter.
A mapping with
<special> fixes this even when
cpoptions wouldn't allow it.