Forum OpenACS Q&A: Re: Ajaxhelper, YUI and xowiki
The require_YUI* methods provide an xowiki-specific configuration for all YUI needs in xowiki and friends. These functions control as well the YUI version numbers. The preconfigured version is YUI 2.7.0. In general, i would not recommend to mix YUI versions. Not all newer YUI versions are fully upward compatible, i had to step back e.g. from 2.8.* to 2.7.0 due to changes in drag and drop. If you use multiple YUI components from different YUI versions on a single page, you are probably asking for troubles.
According to the YUI3 docs, YUI3 is completely encapsulated (they say sandboxed) so that it can co-exist safely with other instances of YUI3 and various YUI2 versions. However, I am in no hurry to create additional problems for myself!
I think I will thrash this through using YUI2 and worry about migrating to YUI3 later.