I'm not sure if this is what you're referring to or not, but do you mean MySpace's planned implementation of Caja ( http://code.google.com/p/google-caja/ ) to scrub / sanitize user generated javascript? Caja would have a problem with all of the major libraries at the current time (YUI, JQuery...

I noticed that my HTML ids and classes are automatically prefixed with "DOM-PREFIX-" when Caja is enabled. This presents a serious impediment to manipulating the DOM. For instance, if I have .red {color: #F00} in my CSS definition and then add <p class="red">...</p> via...