Spaces in mappings: where to put them and where not?

Question

The question is actually rather short, don't be afraid. :-)

I'm Russian, and so to tweak Vim in a way it will understand its commands even if a Russian language is currently active, I have the following part in my vimrc:

set keymap=russian-jcukenwin " jcukenwin for Windows and Linux,
                             " jcukenmac for macOS

set iminsert=0
set imsearch=0

set laststatus=2

" To change the color of statusline when keyboard layout is changed
function MyKeyMapHighlight()
  if &iminsert == 0
    highlight tabLine    ctermfg=darkBlue guifg=darkBlue guibg=darkGrey
    highlight StatusLine ctermfg=darkBlue guifg=darkBlue guibg=Gray30
  else
    highlight tabLine    ctermfg=darkBlue guifg=darkBlue guibg=darkGrey
    highlight StatusLine ctermfg=darkRed  guifg=darkRed  guibg=Gray30
  endif
endfunction

call MyKeyMapHighlight()
autocmd WinEnter * :call MyKeyMapHighlight()

" To switch languages by using Control-Space instead of C-^ (C-6 on Windows)
cmap <silent> <C-Space> <C-^>
imap <silent> <C-Space> <C-^>X<Esc>:call MyKeyMapHighlight()<CR>a<C-H>
nmap <silent> <C-Space> a<C-^><Esc>:call MyKeyMapHighlight()<CR>
vmap <silent> <C-Space> <Esc>a<C-^><Esc>:call MyKeyMapHighlight()<CR>gv

The only part which interests me currently is mappings. I'm trying to understand where to put and where to not put spaces when we define mappings. For example, if I delete spaces after <C-Space>, it doesn't work.

" Doesn't work
cmap <silent> <C-Space><C-^>
imap <silent> <C-Space><C-^>X<Esc>:call MyKeyMapHighlight()<CR>a<C-H>
nmap <silent> <C-Space>a<C-^><Esc>:call MyKeyMapHighlight()<CR>
vmap <silent> <C-Space><Esc>a<C-^><Esc>:call MyKeyMapHighlight()<CR>gv

1. Why the second version doesn't work?
2. Are there explanations/rules/best practices where to put and not put spaces when we define mappings in Vim?

Answer 1

Why the second version doesn't work?

Because there is nothing mapped to <C-Space><C-^>.

Space separates a sequence of keys and a mapped value.

Are there explanations/rules/best practices where to put and not put spaces when we define mappings in Vim?

:h :map is concise indeed. :map {lhs} {rhs} should tell you that there should be a space between {lhs} and {rhs}. So your first mapping {lhs} is <C-Space> and {rhs} is <C-^>.

Mappings could have arguments (in your case it is <silent>) that should be put before {lhs}. See :h :map-arguments.