Are custom Fluent functions allowed to take arbitrary number of positional arguments? #213

Are custom Fluent functions allowed to accept an arbitrary number of positional arguments, or only a single positional argument?
From reading this code, it appears that an arbitrary number of positional arguments is supported. However, the FluentBundle class seems to restrict the function signature to only one positional argument of type Any. If I’m not mistaken, this looks inconsistent — possibly a bug.
I would expect the type to be Callable[..., "FluentType"], where ... allows an arbitrary number of arguments.