The Joint Committee on Taxation issued a summary of all tax legislation enacted in 2015, which details all legislative modifications and explains Congress's reasons for changes to most provisions. The "General Explanation of Tax Legislation Enacted in 2015",commonly known as the "Blue Book," is available at www.jct.gov/publications.html?func=startdown&id=4874 .
It's only four hundred pages long and by clicking on the link it will be automatically downloaded to your computer. Considering the security of government computers, you might think twice about going there. Besides, it wasn't much of an explanation.