Fantastic, thanks so much for this quick help!
For posterity: In my case, the problem was that the macro I’m working on creates a struct that I wanted to be able to document. However, the struct has to be created inside a double quote, and therefore one can’t simply apply @__doc__ to it. However, one can subsequently simply apply @__doc__ to the symbol that names the new struct, thus obviating the need for any more fancy metaprorgamming.