I created Issue 15427 for the parse_args documentation bug. So let's make this issue just about parsing intermixed arguments.

Yes, if someone would like to provide a patch for this, please create a method "parse_intermixed_args" rather than adding a boolean flag parameter. It should be basically equivalent to this code:

args, remaining_args = optionals.parse_known_args()
args = positionals.parse_args(remaining_args, args)

Except that it should give proper error messages. There should be some tests to make sure both that it parses things as expected and that it gives error messages as expected.