Use setlocal for nrformats

autoload/todo.vim

@@ -29,10 +29,6 @@ function! todo#GetCurpos()
         return getpos('.')
 endfunction
 
-" Increment and Decrement The Priority.
-" TODO: Make nrformats local to buffers of type todo
-:set nf=octal,hex,alpha
-
 function! todo#PrioritizeIncrease()
     normal! 0f)h

 endfunction

ftplugin/todo.vim

@@ -16,11 +16,14 @@ set cpo&vim
 
 " General options {{{1
 " Some options lose their values when window changes. They will be set every
-" time this script is invocated, which is whenever a file of this type is
+" time this script is invoked, which is whenever a file of this type is
 " created or edited.
 setlocal textwidth=0
 setlocal wrapmargin=0
 
+" Increment and decrement the priority use <C-A> and <C-X> on alpha
+setlocal nrformats+=alpha
+
 " Mappings {{{1
 
 nnoremap <silent> <buffer> <Plug>TodotxtIncrementDueDateNormal :<C-u>call <SID>ChangeDueDateWrapper(1, "\<Plug>TodotxtIncrementDueDateNormal")<CR>