Specifically useful here, the output of --help includes the required order for parameters for -S usage.

I think users are likely to end up directly on this page if they're having problems with the built-in server (as in the linked issue) and teaching them where they can find this information right at the commandline (and specific to their version of PHP) is useful.

Many users are not familiar with the common conventions of (*nix) commands.

I think the caveat is helpful, and once aware users can be expected to work out which options likely can be applied when running the built-in server.

I'm open to suggestions for how to modify the documentation to help users in cases like the linked issue, keeping in mind that there are already examples of correct usage on the page.