Ruby on Rails 3.1 Release Notes — Ruby on Rails GuidesHighlights in Rails 3.1: Streaming Reversible Migrations Assets Pipeline jQuery as the default JavaScript library These release notes cover only the major changes. To learn about various bug fixes and changes, please refer to the changelogs or check out the list of commits in the main Rails repository on GitHub. 1 Upgrading to Rails 3.1If you're upgrading an existing application, it's a great idea
