Mac OS X计时应用程序如何跟踪文件

I am curious about how Timing is able to know the amount of time you spend in a particular file. I understand that it needs Accessibility permission, but after that, how is it able to detect what's currently on the screen, plus accessing the path to a given file. I find intriguing, for example, that it knows that I am on Xcode, but how does it know I am working on a specific file, inside Xcode? is able to know t