I am looking at some plugin that happens to be configurable through a curious mapping (e.g. unite.vim):

More advanced configuration example:
    " The prefix key.
    nnoremap    [unite]   <Nop>
    nmap    f [unite]

    nnoremap <silent> [unite]c  :<C-u>UniteWithCurrentDir
            \ -buffer-name=files buffer bookmark file<CR>

What does the [unite] means ?

I understand that it stands for a custom leader/prefix only for the plugin, but what is it's meaning for Vim ?

  • 2
    The way I see it, it's a clever way to create a custom leader. If you only press f in your example, it will be resolved to [unite] (due to the nmap), which in turn resolves to <Nop>, i.e. nothing, but only after the map timeout, or if not followed by one of the defined combinations, such as c, in which case it suddenly turns into [unite]c, which resolves to the mapped command :) Basically, f turns to nothing, but fc turns to the mapped command. [unite] is just a convenient placeholder, you can use other text if you want. Vim won't interpret its characters individually. – VanLaser Mar 1 '16 at 0:38
  • OK I see, this is indeed really clever. What about the [ square bracket ] ? Does they means "treats this as one symbol" ? – nobe4 Mar 1 '16 at 0:50
  • 2
    Nope, they are no more special than any other characters. They are for your eyes only, to look like a prefix key. :) – VanLaser Mar 1 '16 at 0:51
  • So I can imagine nnoremap myprefix <nop> and then using myprefix anywhere ? or using {} instead ? – nobe4 Mar 1 '16 at 1:17
  • 1
    Do it, please :) There is a side-effect of choosing a certain 'prefix' - e.g. [unite] could affect a map defined in the same buffer, made from its first letters (e.g. [u) in that Vim will now wait to see if you type n after it, or not. – VanLaser Mar 1 '16 at 8:36

After discussion with VanLaser, it seems that the [unite] mapping is used only with a combination of another key.

Let's break down the mappings:

nnoremap    [unite]   <Nop>

Map [unite] to nothing.

nmap    f [unite]

Map f to [unite]. At this point if we press f, nothing will happen, as [unite] is mapped to <nop>.

But when we add a [unite]-based mapping:

nnoremap <silent> [unite]c  :<C-u>UniteWithCurrentDir ...

Then the [unite]c (which will be triggered by pressing fc) will call the desired command. If the f key is pressed alone, after the map timeout, nothing will append as it will be translated to [unite] alone.

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