doc: xdg, MAINTAIN.md, channel-id, job control

- tutor: emphasize K

runtime/doc/vim_diff.txt

@@ -205,19 +205,8 @@ certain features removed/added at compile-time. |feature-compile|
 If a Python interpreter is available on your `$PATH`, |:python| and |:python3|
 are always available and may be used simultaneously. See |provider-python|.
 
-|:!| does not support "interactive" commands. Use |:terminal| instead.
-(GUI Vim has a similar limitation, see ":help gui-pty" in Vim.)
-
-:!start is not special-cased on Windows.
-
-|system()| does not support writing/reading "backgrounded" commands. |E5677|
-
 |:redir| nested in |execute()| works.
 
-Nvim may throttle (skip) messages from shell commands (|:!|, |:grep|, |:make|)
-if there is too much output. No data is lost, this only affects display and
-makes things faster. |:terminal| output is never throttled.
-
 |mkdir()| behaviour changed:
 1. Assuming /tmp/foo does not exist and /tmp can be written to
    mkdir('/tmp/foo/bar', 'p', 0700) will create both /tmp/foo and /tmp/foo/bar 
@@ -323,6 +312,22 @@ Normal commands:
 Options:
   'ttimeout', 'ttimeoutlen' behavior was simplified
 
+Shell:
+  Shell output (|:!|, |:make|, …) is always routed through the UI, so it
+  cannot "mess up" the screen. (You can still use "chansend(v:stderr,…)" if
+  you want to mess up the screen :)
+
+  Nvim throttles (skips) messages from shell commands (|:!|, |:grep|, |:make|)
+  if there is too much output. No data is lost, this only affects display and
+  improves performance. |:terminal| output is never throttled.
+
+  |:!| does not support "interactive" commands. Use |:terminal| instead.
+  (GUI Vim has a similar limitation, see ":help gui-pty" in Vim.)
+
+  :!start is not special-cased on Windows.
+
+  |system()| does not support writing/reading "backgrounded" commands. |E5677|
+
 Startup:
   |-e| and |-es| invoke the same "improved Ex mode" as -E and -Es.
   |-E| and |-Es| reads stdin as text (into buffer 1).