"The world of books is the most remarkable creation of man. Nothing else that he builds ever lasts. Monuments fall; nations perish; civilizations grow old and die out; and, after an era of darkness, new races build others."
The target attribute specifies where to open the linked document.
I know. That's why this use doesn't seem to make sense to me. Maybe it's useful if you have a ton of such links and they'll all open into the same window as the first? In any case, it can safely be left out. Links open fine without a target attribute.