" F12 to add line numbers to the selected lines
vnoremap <F12> :s/^/=line(".").". "
" The same as above but numbers from 1 to n
"vnoremap <F12> :s/^/=line(".")+1-line("'<").". "

" Shift-F12 to remove any numbers from the beginning of selected lines
vnoremap <S-F12> :s/^d. /