JQuery vs MooTools
Dadepo Aderemi on why he choose JQuery over MooTools for his JS Framework
Compared to mootools, Jquery’s Selectors makes accessing the Dom such a breeze. Borrowing syntax from CSS and Xpath you can burrow all the way down or climb all the way up the DOM with a succinct amount of code.
http://geekabyte.blogspot.com/2007/06/ditching-mootools-for-jquery.html
Think twice. Why would you need to traverse the DOM all the way up or down? It-s inefficient least to say.
What if you were looking to build an array of a particular class or Tag, then you would need to work down the DOM and pickup all the elements.