I am struggling to understand some code that uses the function
Format.kfprintf, I understand how
utop # Format.fprintf Format.std_formatter "@[%s: [%d]@]@." "test" 1;; test:  - : unit = ()
but I can not find how to use
Format.kfprintf, I think that like
Printf.ksprintf, it is used when you want to create function that can handle different formats (http://form-ocaml.forge.ocamlcore.org/posts/ksprintf.html) but I am stuck.
Can someone provide me a simple example?
Format.kprinft -> Format.kfprintf