Markdown checkboxes

autocmd FileType markdown let b:switch_custom_definitions =
    \ [
    \   { '\v^(\s*[*+-] )?\[ \]': '\1[x]',
    \     '\v^(\s*[*+-] )?\[x\]': '\1[-]',
    \     '\v^(\s*[*+-] )?\[-\]': '\1[ ]',
    \   },
    \   { '\v^(\s*\d+\. )?\[ \]': '\1[x]',
    \     '\v^(\s*\d+\. )?\[x\]': '\1[-]',
    \     '\v^(\s*\d+\. )?\[-\]': '\1[ ]',
    \   },
    \ ]

• - [ ] → - [x] → - [-] → loops back to - [ ]
• + [ ] → + [x] → + [-] → loops back to + [ ]
• * [ ] → * [x] → * [-] → loops back to * [ ]
• 1. [ ] → 1. [x] → 1. [-] → loops back to 1. [ ]