Apple events are the message-based interprocess communication mechanism in Mac OS, first making an appearance in System 7 and supported by every version of the classic Mac OS since then and by macOS. Apple events describe "high-level" events such as "open document" or "print file", whereas earlier OSs had supported much more basic events, namely "click" and "keypress". Apple events form the basis of the Mac OS scripting system, the Open Scripting Architecture.