My 24 yo brother is just entering the stage of life where his friends are getting married, and he and his girlfriend were invited to an AHR happening next weekend. (I know about this because it's in our city and I'll be seeing him on his trip.)
However, he keeps calling it a "shower," which I find hilarious. I suppose it could be a co-ed shower, held at a winery, expected to go late into the night/early morning, but what he told me of the invite ("come celebrate our marriage") makes me think AHR. I can just see his thought process: "It's obviously not their wedding, but it's a party definitely related to their wedding... must be a shower!" Maybe they were so gracious as to include registry info so as to further confuse the young man.