See https://www.facebook.com/dreiss/posts/10152231659206208. I added this "bizarre Facebook-ism" to the set of ordered list characters in T3797, but apparently the intent of these "1/" lists is to avoid automatic formatting. I don't fully understand any part of this, but this list style is used only at Facebook, and automatically formatting these lists enjoys little support there (25 against, 2 for, 29 neutral).

Updated and executed unit tests.