anchor.diff:  
   Note that these commands are available in interactive command mode, but are
   not that useful in this context.
  +
  +FIFO Buffer
  +-----------
  +
  +the *edit* command can take a -fifo parameter:
  +:edit -fifo <filename> <buffername>
  +in this case, a buffer named <buffername> is created which reads its content
  +from <filename>. When filename is appended to, the buffer is automatically
  +updated.
  +This is very useful for running some commands asynchronously while displaying
  +their result in a buffer. See rc/make.kak and rc/grep.kak for examples.
  
positive.code: 
   * *kak_selection*: content of the last selection
   * *kak_bufname*: name of the current buffer
   * *kak_opt_name*: value of option name
   * *kak_reg_x*: value of register x
  
  
negative.code: def can also takes some flags:
   * *-env-params*: pass parameters given to commands in the environement as
                    kak_paramN with N the parameter number
   * *-shell-params*: pass parameters given to commands as positional parameters
                      to any shell expansions used in the command.
   * *-shell-completion*: following string is a shell command which takes
                          parameters as positional params and output one
                          completion candidate per line.
   * *-allow-override*: allow the new command to replace an exisiting one
                        with the same name.
  