The documentation content looks good, just a few minor changes with the main content.

I think showcasing optional arguments would be much better on its own page instead of at the bottom of arguments.md. Can we please create a new page (e.g. optional_arguments.md), and place that above the "Listed arguments" section in SUMMARY.md.

The new page should be titled "Optional arguments" (get rid of "/Different" from the title, I don't want that anymore). I'd like some explanation about optional arguments and a block of code at the top showing the various withOptionalArguments() methods.

If you're struggling to meet these requirements, just let me know and I'll help out.

• So, we remove the section Optional/Different Arguments from arguments.md?
• We are creating a new page optional_arguments.md?

• So, we remove the section Optional/Different Arguments from arguments.md?

Yes 👍

• We are creating a new page optional_arguments.md?

Yes 👍

In #360, there was an idea of being able to retrieve "default" values from optional arguments:

It is useful to be able to access arguments by node name, rather than by index - especially in the case of using optional arguments:

(CommandSender sender, Map<String, Object> args) -> {
    String input = (String) args.get("blah");
    int amount = (int) args.getOrDefault("amount", 1);
}

Since we're adding all of the optional argument stuff now, it may be worth considering adding this to this PR. I think it's a good idea to add this to simplify null checks for arguments you know are going to be optional arguments:

new CommandAPICommand("sayhi")
    .withOptionalArguments(new PlayerArgument("target"))
    .executesPlayer((player, args) -> {
        Player target = (Player) args.getOrDefault("target", player);
        target.sendMessage("Hi!");
    })
    .register();

It may also be worth considering implementing a Supplier<?> overload as well:

new CommandAPICommand("sayhi")
    .withOptionalArguments(new PlayerArgument("target"))
    .executesPlayer((player, args) -> {
        Player target = (Player) args.getOrDefault("target", () -> getBestFriend(player));
        target.sendMessage("Hi!");
    })
    .register();

This could also safely handle the index overload without an index out of bounds exception.

You need to help me with the Supplier part though. I am not too familiar with them.
Would I implement them like this:

public Object getOrDefault(int index, Supplier<?> defaultValue)

You need to help me with the Supplier part though. I am not too familiar with them. Would I implement them like this:

public Object getOrDefault(int index, Supplier<?> defaultValue)

Yes, that's precisely it. A Supplier<T> is effectively identical to Function<Void, T> - it's a function that doesn't have any input parameters, but returns a value. You can call the supplier using supplier.get().