Lots of AppleScript and Automator changes were introduced with OS X 10.9 Mavericks. Here are links to official Apple technical resources that discuss some of them...
- AppleScript Release Notes (Updated for OS X 10.9 Mavericks)
- AppleScript Language Guide (Updated for OS X 10.9 Mavericks)
- Technical Q&A QA1802 (Adopting Scripting Targets for Composing Mail)
- OS X: Using AppleScript with Accessibility and Security features in Mavericks
- WWDC 2013: Session 416: Introducing AppleScript Libraries
- WWDC 2013: Session 417: Automation Update
For a general overview of the automation changes in Mavericks, visit macosxautomation.com (not hosted by Apple Inc.).