Better/complete documentation of sys.stdin/stdout/stderr default behavior

See https://docs.python.org/3/library/sys.html?highlight=stdin#sys.stdin
The default behavior of sys.stdin/stdout/stderr is not fully documented (e.g. the default newline mode, depending on OS), and the current existing documentation is a lot more difficult to understand than it would need to be, referring to internal c-api settings instead of explaining in clear language what is going.

Given how important this information is and given that the behavior of sys.stdin/out/err is surprisingly DIFFERENT from what the default would be if open with default settings would be used, making the documentation more complete and easier to understand would be rather important. The number of questions on stackoverlow (partly with incorrect or hard to verify answers) about this is a good indicator of how confusing and important this matter is.

Start with the sys.stdin, sys.stdout, and sys.stderr section at the linked Python documentation page, then compare its description with the behavior of open using default settings across operating systems. The work is done when the default newline behavior and other relevant differences are explained clearly and accurately without relying on internal C API terminology.