You can go backNow when you click on a link in a book a tiny link appears in the lower left corner of the page allowing you go back to the page from whence you came. When you go back, there is then a link in the lower right corner letting you go back to where you came back from (that is, forward).
This is a huge improvement, and makes footnotes/endnotes and links in general MUCH more useful. I love it.
Imagine you're on a links page in Walden:
You click on the line "I have always been regretting that I was not as wise as the day I was born." and jump to the page that contains that link.
In the bottom-left corner of the new page, you see "Back to page xx".
If you click on it, you'll go back to the page you came from. And now on the page you came from, you'll see a light gray link in the bottom-right corner that lets you go forward again to the page you had clicked to go to.