This is an abridged version of the printed version. In particular, theoretical considerations, examples, motivation and methodological issues were substantially abbreviated. In contrast, the review of past studies has been copied in full so as to invite readers to expand it.

The system allows you to 1) contribute to the article, 2) adapt the view to your interests by tailoring the scope of the article, and 3) adjust dynamically the level of detail you wish to see.

Furthermore, navigation through the article is made easier by using Figures to travel directly to places of interest, by using Tables to overview sections of the article, and by using the TOC to both travel and see where you are.

I' m indebted to several of my students for helping create this system. In particular, Hila Yefet did most of the programming and Gilat Bango prepared and edited the materials. Orit Harel is researching user's behavior (a few cookies track navigation paths). In addition, Dana Barnea-Rashty produced the graphics.