anchor.diff:  ...will find none of Kakoune's special environment variables, but:
   
   ----
  -echo %sh{ env | grep ^kak_ # $kak_session }
  -----
  -
  -...will find the `$kak_session` variable because it was mentioned inside the
  -shell script, even just in a comment.
  +echo %sh{ env | grep ^kak_ # kak_session }
  +----
  +
  +...will find the `$kak_session` variable because it was mentioned by name
  +in a comment, even though it wasn't directly used.
   
   TIP: These environment variables are also available in other contexts where
   Kakoune uses a shell command, such as the `|`, `!` or `$` normal mode commands
  
positive.code: `{}` are most common. For example, the command `echo %val{session}` will
  echo the ID of the current Kakoune session.
  
  Expansions are processed when unquoted and anywhere inside double-quoted or
  %-strings, but not inside unquoted words, inside single-quoted strings, or
  inside other expansions. So:
  
  * `echo %val{session}` echoes the current session ID
  
  
negative.code: 
  * `echo "x%val{session}x"` echoes the current session ID, surrounded by `x`
  
  * `echo %{%val{session}}"` echoes the the literal text `%val{session}`
  
  * `echo %sh{ echo %val{session} }"` echoes the literal text `%val{session}`
  
  Like "variable expansion" and "command substitution" in shell programming,
  Kakoune expansions can expand to multiple "words" - that is, separate
  arguments on the resulting command-line. However, unlike shell programming,
  Kakoune expansions cannot _accidentally_ expand to multiple words, even if
  the expansion contains whitespace or other special characters. While in
  shell-programming it's good practice to always wrap expansions in
  double-quotes, in Kakoune it's perfectly safe to leave expansions unquoted.
  
  == Argument expansions
  
  