I.e. X11 working in same way as Windows, OS/2, BeOS, MacOS, OSX, etc.
No, it's not. OS X has GUI isolation, an application cannot read keystrokes or read other application's contents, unless you explicitly give permission to do so. This is the reason why applications that can do more, such as Alfred, require you to explicitly enable these rights in the Privacy section of the Security & Privacy prefpane.
Windows also has GUI isolation (UIPI), but it's a bit murkier. As far as I understand, lower-privileged applications cannot read events from higher-privileged applications.
No, it's not. OS X has GUI isolation, an application cannot read keystrokes or read other application's contents, unless you explicitly give permission to do so. This is the reason why applications that can do more, such as Alfred, require you to explicitly enable these rights in the Privacy section of the Security & Privacy prefpane.
Windows also has GUI isolation (UIPI), but it's a bit murkier. As far as I understand, lower-privileged applications cannot read events from higher-privileged applications.
https://msdn.microsoft.com/en-us/library/bb625963.aspx