Forgot to add: I haven't looked at the docs yet, but I agree they should be clear on this issue.

The docs should say: for types that implement the documented mini-language, "s" is the same as "". It's just that not all types implement the mini-language (like datetime, and probably many non-standard, user-defined types).

If they don't say that, can you open a separate documentation issue? Thanks.

Or, maybe the problem is that the docs make it seem like all types do (or should?) implement the mini-language? That's definitely not true, and they shouldn't say that.