Seems like this requires you to select some text (which includes some text that's been hidden using CSS tricks) and copy it. So it's not like the website can just arbitrary write to your clipboard without your interaction? (Still, this is kinda scary and I didn't know about this.)

They can append the message to whatever you'll actually want to copy, which is how websites used to do things like this.

- Copied from https://news.ycombinator.com/item?id=26590437

Really interesting(and terrifying) reads, thank you.