Extensibility and Automation Changes in OS X Yosemite
J Thoendell stashed this in Apps
OSA is a mechanism for inter-app communication between Mac apps, and it is what AppleScript and JXA are built on. The communication occurs by sending “Apple Events” – messages which include commands or data – back and forth between apps. OSA allow Mac developers to create scriptable applications, and it allows any user who knows AppleScript (or, now, JXA) to automate these applications.