/// Appends the new argument to the list of arguments.
///
/// **NOTE:** It returns an `error.DuplicatePositionalArgIndex` when attempting
/// to append two positional arguments with the same index. See the examples below.
///
/// ## Examples
///
/// ```zig
/// var app = App.init(allocator, "myapp", "My app description");
/// defer app.deinit();
///
/// var root = app.rootCommand();
/// try root.addArg(Arg.booleanOption("version", 'v', "Show version number"));
///
/// var test = app.createCommand("test", "Run test");
/// try test.addArg(Arg.positional("FILE", null, null));
/// ```
///
/// Appending two positional arguments with the same index.
///
/// ```zig
/// var app = App.init(allocator, "myapp", "My app description");
/// defer app.deinit();
///
/// var root = app.rootCommand();
/// try root.addArg(Arg.positional("FIRST", null, 1));
/// // Returns `error.DuplicatePositionalArgIndex`.
/// try root.addArg(Arg.positional("SECOND", null, 1));
/// ```
pub fn addArg(self: *Command, arg: Arg) !void { ... }

/// Appends multiple arguments to the list of arguments.
///
/// ## Examples
///
/// ```zig
/// var app = App.init(allocator, "myapp", "My app description");
/// defer app.deinit();
///
/// var root = app.rootCommand();
/// try root.addArgs(&[_]Arg {
///     Arg.singleValueOption("firstname", 'f', "First name"),
///     Arg.singleValueOption("lastname", 'l', "Last name"),
/// });
///
/// var address = app.createCommand("address", "Address");
/// try address.addArgs(&[_]Arg {
///     Arg.singleValueOption("street", 's', "Street name"),
///     Arg.singleValueOption("postal", 'p', "Postal code"),
/// });
/// ```
pub fn addArgs(self: *Command, args: []const Arg) !void {
    for (args) |arg| try self.addArg(arg);
}