'BufNewFile,BufFilePre,BufRead' or simply 'BufFilePre,BufRead' when detecting a filetype?

Question

The following snippet is from the vim-pandoc-syntax plugin README:

If you want to use vim-pandoc-syntax without vim-pandoc, you'll need to tell Vim to load it for certain files. Just add something like this to your vimrc:

augroup pandoc_syntax
    au! BufNewFile,BufFilePre,BufRead *.md set filetype=markdown.pandoc
augroup END

What might be the reason to use BufNewFile here? Isn't it that BufFilePre and BufRead are sufficient?

When we create a new empty buffer, its filetype value is blank in either case.

Answer 1

1. Using :h ftdetect is preferred over direct approach. This way you add commands into predefined filetypedetect augroup and so you don't need to create yet another one.

2. BufNewFile is needed to handle :e newfile.md and such. And, no, in this case a newly created file can get a correct filetype even though it has neither contents nor it was read from disk.

3. BufFilePre is not useful here. I guess you mean BufFilePost instead. But it's only triggered after :file or :saveas commands, so usually no one cares.