anchor.diff:  have the following format.
   
   ----
  -line.column[+len]@timestamp:candidate1|desc1|menu1:candidate2|desc2|menu2:...
  +line.column[+len]@timestamp candidate1|desc1|menu1 candidate2|desc2|menu2 ...
   ----
   
   the first element of this string list specify where and when this completion
  
positive.code: -----
  
  This is a very simple example, most of the time, the echo command will as
  well contains
  
  -----
  set buffer filetype <...>
  
negative.code: ==========================================
  
  In order to interact with the external world, Kakoune uses the shell, mainly
  through the +%sh{ ... }+ string type, and its control socket.
  
  Basic interaction
  -----------------
  