Sizzle and Peppy Selector Engines in MooTools
A few weeks back I touched on how you could implement the Peppy and Sizzle selector engines in MooTools. Both posts showed how to remove the default Moo engine from use and instead make each respective selector engine the one and only. It doesn't have to be that way. You could use all three engines within the page as well.
Peppy, Sizzle, and Moo Together
Why do this? Each engine has its advantages. Sizzle generally does better with Internet Explorer so if you detect that the user is using IE, you may want to use Sizzle to grab the elements instead.
In most cases the overhead of bringing in each engine makes this strategy overkill. It's definitely an option though.