anchor.diff:  
   == Value expansions
   
  -Expansions with the type `val` can be used in various places, depending on the
  -specific value.
  -
  -The following expansions are supported:
  +Expansions with the type `val` give access to Kakoune internal data that is
  +not stored in an option or a register. Some value expansions can only be used
  +in certain contexts, like `%val{hook_param}` that expands to the parameter
  +string of the currently-executing hook, and is not available outside a hook.
  +
  +The following expansions are supported (with required context _in italics_):
   
   *%val{buffile}*::
       _in buffer scope_ +
  
positive.code: ...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.
  
  TIP: These environment variables are also available in other contexts where
  Kakoune uses a shell command, such as the `|`, `!` or `$` normal mode commands
  
negative.code:      expands to argument number _n_ of the current command
  
  *%arg{@}*::
      expands to all the arguments of the current command, as individual words
  
  == Option expansions
  
  