I know in a post two years ago that somebody was already asking about
The answer was that they don’t work. I just encountered this in the calendar text and footer. I understand maybe in the first version of YCBM you maybe used a fresh library or implemented markdown yourselves but now Markdown is so ubiquitous that there are a lot of good libraries and it’s weird to have a semi-broken version of Markdown URLs (I can’t imagine Markdown would be very popular if it only supported certain types of links but not others!).