From an In Custodia Legis Blog Post by Andrew Weber:
One of our goals with the Twitter account is to provide timely alerts about legislative developments and, with this change, now we can do that directly from the homepage.
We’ve added a new way to browse legislation: by subject terms. If you browse through the list you can see how many items have been tagged with each subject during this Congress. A sample of the terms available to browse by includes education, energy, immigration, health, and law.