It's a new feature that allows you to quickly and easily edit links you embed as words in your post. You can make the link a clickable word or phrase instead of just pasting it in (which was always possible, but you couldn't edit it as easily as you can now).
So basically this:
Click for article
Versus having to paste it in like this:
https://www.backyardchickens.com/articles/the-beginners-guide-to-incubation.73350/
And the new feature makes it so I can edit the words of the link very easily.
Ah. Thank you, Sinsei.