Mix-Pasting And Deleting Selection

I thought of a possibility to paste one track on another but have the second one not disappear, but mix in with the first. Could be interesting for some purposes, maybe.

The other thing is the deletion of a selection. I haven’t figured it out, and I also checked the key commands, nothing there. Those could still be expanded a lot, btw. Backspace and Delete will only work for one line, but I can’t delete a quarter of the screen in one go.