I have never heard of alt+left, and I’ve been using the Internet since Mosaic was all the rage. Shame on me, it seems to be implemented in all browsers. How could I have missed it?

Because sponsoring doesn’t infringe on privacy, is usually controlled by the channel, and is often relevant.

Or even worse:

Thanks. Send a complete log of every software on your system, two videos of the bugs in action, and a detailed analysis of what you’ve had for breakfast.