NY Times Built In Dictionary

If you go to an actual article or column on the NY Times Web site, but not a box with the first paragraph of the article on the homepage, and then you select a word by clicking and dragging over it, a question mark will appear. If you click on the question mark, it will ask whether you want a definition of the word. This is remarkably quick and convenient, a very nice feature indeed. The Kindle has something similar but at least on my original Kindle, it is not a fast. I wonder what it would take to produce this sort of functionality more broadly. It would really help language acquisition and encourage people to read online because they could more readily get past their own blockages.