I have the following dysfunctional mapping
" Capitalise each word in selection vmap gw :'<,'>s/\<./\u&/g<CR>
which should do what the comment says. But when I use it, vim reports
E488: Trailing characters. It works when I leave out the selection marks
'<,'>, but then it applies to the whole line.
I suspect I need to escape something here, but the help page only lists some other characters which must be escaped.