What sites have you visited?

As described by lcamtuf, mix-blend-mode can be used to give some indication of a user's browsing history. lcamtuf explains how this can be used in a phishing attack by tricking the user into clicking on the element that corresponds to their visited links.

See also: Github spec discussion.

This is a simple example of highlighting basead on visited links

!CNN
!hackernews		 CNN
!hackernews		 !CNN
hackernews		 CNN
hackernews