Thank you. I came across this post several hours ago, was confused and, like you, found the explanatory link which should have been posted and was about to reply with it but then got a phone call.

I love HN but the frequency of 'mystery links' is too high. I assume it's either because the poster is so familiar with the relevant domain they forget others aren't or, more annoying, they know many will be puzzled but assume "it's SO great, everyone will be instantly captivated and spend several minutes on a magical journey until they work it out." Unfortunately, sometimes I'm kind of busy and just bookmarking interesting stuff to come back to. Other times, it might have been something I'd be interested in, but I don't find the first minute quite as magical as the poster and bounce before ever knowing what the hell it is.