Maybe is it a good place to post such a question here ?

 Not an OCaml specific question, however I'm trying to feed properly the 'doc' field for 'Arg.parse'.

Unix command :
man man
says :

bold text          type exactly as shown.
italic text        replace with appropriate argument.
[-abc]             any or all arguments within [ ] are optional.
-a|-b              options delimited by | cannot be used together.
argument ...       argument is repeatable.
[expression] ...   entire expression within [ ] is repeatable.

(However, outside a man page, when we type --help, there is nothing bold neither italic.)

Please is there additional documentation / examples about documentation conventions somewhere ?

  For example, how to describe, in the 'usage', a list of unrepeatable 'unit' options - their order being significant ?
(At this syntactic level, is it even possible to describe that some option cannot be repeated ?)
  Can I use '|' to say that, if any anonymous argument is provided, it will be impossible to specify some integer parameters ?

Any light ?