this advice would not be helpful for an openbsd system

Sorry, I wasn't aware of that. BSD usually has excellent pan man pages.

Here's the relevant section in the Linux one:

The following conventions apply to the SYNOPSIS section and can be used as a guide in other  sections.

       **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.

The destination, with or without the username to connect as, may not seem like an “argument” to a new user since it doesn’t have a dash before it like the example does

Then the new user should real the ssh manpage which very clearly specifies that it is.