"Rules" that terminal programs follow

Terminal behavior is mostly consistent even without explicit standards, with users often expecting noninteractive programs to quit on Ctrl-C, TUIs to exit on Ctrl-Q, REPLs to end on Ctrl-D when they hit an empty line, and applications to stick to 16 ANSI colors for better compatibility with users' terminal settings; though exceptions exist, these conventions help users predict program behavior, despite the lack of official guidelines.