It's a misuse of the Python Ellipsis, though PEP has no opinion on it. The Ellipsis is "Special value used mostly in conjunction with extended slicing syntax for user-defined container data types."
In other words, it happens to work and look neat, but pass is the correct way to do it.
Ellipses is actually used in quite a few places. See the answers and comments on this stackoverflow post[0]. The usage most similar to what I have in the magentic examples is with the `@overload` decorator in the typing module[1].
With that said, you are free to put any code in the function body including `pass` or just a docstring or even `raise NotImplementedError` - it will not be executed. Using Ellipses satisfies VSCode/pyright type checking and seemed neatest to me for the examples and docs. I have some additional notes on this in the README[2].
In other words, it happens to work and look neat, but pass is the correct way to do it.