The missing } is a mistake, we'll correct that in the next version (as it's a breaking change).
There's currently no macro for FK fields. The problem is that when the attribute macro's are handled, the handler doesn't know for which element it is, it just gets strings passed in for various macro elements and it then will replace them, but that's it. So it's not able to transform a macro in a series of fk field names at that level at this point.
Is this a requirement for your application? We can add it in the future, but of course that is of no use for you now.