Right! Ok, thank you.
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.
R.