The option provides a callback (of type GLib.OptionArgFunc) to parse the extra argument.
The option takes a double argument. The argument can be formatted either for the user's locale or for the "C" locale. Since 2.12
The option takes a filename as argument, which will be in the GLib filename encoding rather than UTF-8.
The option takes a filename as argument, multiple uses of the option are collected into an array of strings.
The option takes an integer argument.
The option takes a 64-bit integer. Like
GLib.OptionArg.INT but for larger numbers. The number can be in
decimal base, or in hexadecimal (when prefixed with 0x, for
example, 0xffffffff). Since 2.12
No extra argument. This is useful for simple flags or booleans.
The option takes a UTF-8 string argument.
The option takes a string argument, multiple uses of the option are collected into an array of strings.
The GLib.OptionArg enum values determine which type of extra argument the options expect to find. If an option expects an extra argument, it can be specified in several ways; with a short option:
-x arg, with a long option:--name argor combined in a single argument:--name=arg.