I really love this feature in Sierra, I just wish it was available on more sites than just YouTube. I’ve not come across any anyway. I noticed that embedded Youtube videos on other sites, such as MR don’t utilise this just yet, as I tried it on here for the High Sierra feature video. Picture-in-Picture has been great for things like the UK General Election and the unfortunate terrorist atrocities we’ve had over this side of the pond, and the Grenfell Tower fire incident. But it’s also good for watching my subscribed channels while using other websites, and not having to have another clunky window open just for Youtube is a huge plus. My apologies for being this late to show my appreciation but it’s something I’ve only started recently using really. Thanks and nice job Apple.