2021 Update - Good News 
There’s a detailed answer here: .Site.Author Usage? - #8 by jmooring
No official docs, but that guy put some docs together by inspecting how index.xml was built, so it’s probably as good as can be hoped for.
There’s a detailed answer here: .Site.Author Usage? - #8 by jmooring
No official docs, but that guy put some docs together by inspecting how index.xml was built, so it’s probably as good as can be hoped for.