Stuart Langridge: @adactio ooh, that's cool. Why not just use pingback? I assume the answer is "XML-RPC, man, why", for which I apologise :)

@sil @adactio fwiw, pingback was extremely valuable prior art for webmention, the first indieweb comment implementation used pingbacks, and some indieweb sites (my own included) support comments using pingback as the notification transport, often using webmention.io as a proxy