The Joint Committee on Taxation’s Technical Explanation of the exit tax is here as a PDF. Actually, the part you’re interested in starts on Page 36, so skip the rest of it.
I’ll give you a plain text excerpt shortly, plus the text of new Section 877A (the part of the Internal Revenue Code that imposes the exit tax when you give up your U.S. passport or green card). And I’ll do a boil-down Babelfish translation of tax jargon to English. But for now, read this turgid prose straight from Congressional staffers and Treasury Department ghostwriters.