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http://wiki.jqueryui.com/w/request-accessHow do I become able to make comments on your tree design page?
Progress has never started in earnest on this particular plugin, at least not on the part of developers on the jQuery UI team, because it has yet to be prioritized enough to move all the way through the early planning stages. The work that has been accomplished to date has been mostly community member contributions we wanted to make sure we didn't miss out on, even if it was ahead of our timeline. This is the idea behind our wiki pages. SeeThe last comment on there was made on 27th May 2010. Does this mean progress has stalled?
Lastly, most of your points above are very good questions. They each deserve informed and proper consideration. However, if we break everything down to sub-problems I don't see a deal breaker here.
I am not suggesting this is a trivial project - but I feel the value that would be gained from a Tree widget means that the effort involved would be worth it.
What would it take to inject some momentum into this project?