bboo baz
        will be interpreted the same as
          -ablah -bboo -- foo bar baz
        If this flag were false, that command line would be interpreted as
          -ablah -- foo bar -bboo baz
        -- ie. we stop processing options as soon as we see the first
        non-option argument.  (This is the tradition followed by
        Python's getopt module, Perl's Getopt::Std, and other argument-
        parsing libraries, but it is generally annoying to users.)

      process_default_values : bool = true
        if true, option default values are processed similarly to option
        values from the command line: that is, they are passed to the
        type-checking function for the option's type (as long as the
        default value is a string).  (This really only matters if you
        have defined custom types; see SF bug #955889.)  Set it to false
        to restore the behaviour of Optik 1.4.1 and earlier.

      rargs : [string]
        the argument list currently being parsed.  Only set when
        parse_args() is active, and continually trimmed down as
        we consume arguments.  Mainly there for the benefit of
        callback options.
      largs : [string]
        the list of leftover arguments that we have skipped while
        parsing options.  If allow_interspersed_args is false, this
        list is always empty.
      values : Values
        the set of option values currently being accumulated.  Only
        set when parse_args() is active.  Also mainly for callbacks.

    Because of the 'rargs', 'largs', and 'values' attributes,
    OptionParser is not thread-safe.  If, for some perverse reason, you
    need to parse command-line arguments simultaneously in different
    threads, use different OptionParser instances.

    Nr.