It's not something that vim explicitly allows, it's a side-effect of running the editor in a terminal. When you paste into a terminal, it's as if the keys are a

It's not something that vim explicitly allows, it's a side-effect of running the editor in a terminal. When you paste into a terminal, it's as if the keys are actually being pressed, rather than just text inserted. The proper way of pasting into vim, which doesn't have this problem, is "+p (as mentioned in the article).