Update

vimscript.md

@@ -110,14 +110,38 @@ function! infect(...)
 endfunction
 ```
 
-Commands
+Custom commands
---------
+---------------
+
+Custom commands start with uppercase letters. The `!` redefines a command if it already exists.
 
 ```vim
-command! Save set fo=want tw=80 nowrap
+command! Save :set fo=want tw=80 nowrap
-command! Save call s:Foo()
 ```
 
+### Commands calling functions
+
+```vim
+command! Save call script#foo()
+function! script#foo()
+  ...
+endfunction
+```
+
+### Commands with arguments
+
+```vim
+command! -nargs=? Save call script#foo(<args>
+```
+
+| What | What |
+| ---- | ---- |
+| `-nargs=0` | 0 arguments, default |
+| `-nargs=1` | 1 argument, includes spaces |
+| `-nargs=?` | 0 or 1 argument |
+| `-nargs=*` | 0+ arguments, space separated |
+| `-nargs=+` | 1+ arguments, space reparated |
+
 Flow
 ----