One of the more challenging aspects in creating the interactive app for exploring the United States Constitution was the lack of an XML version of the U.S. Constitution.
I looked around on the web a bit, but I was unable to find one. (Perhaps I missed it, please let me know). This in contrast to the Titles of the U.S. Code which have been released in .xml Format.(Edit: Update – Some time after I wrote this, Congress released an Official version of the US Constitution in xml – located here. You may prefer that to my unofficial version below.)Structuring the law as data in XML (or some other structured format) is what permits us to create interesting visualizations like the above, or those here and here.