This page is both a demo and a descriptive page. Hover with the mouse over the highlighted text areas to see other user's annotations. If you are logged in at Diigo.com at the same time (perhaps in a different tab/window, or one that is already closed without logging out), you can add comments to others annotations. The effect is that when anyone comes to that page, they see yours and others highlights and annotations/comments. Very powerful and useful way of sharing information, opinions, etc. Supplements normal bookmarking excellently.