const default_mode: type = switch (builtin.os.tag) {
        .windows => 0,
        .wasi => 0,
        else => 0o666,
    };

This is the default mode given to POSIX operating systems for creating files. 0o666 is “-rw-rw-rw-” which is counter-intuitive at first, since most people would expect “-rw-r–r–”, for example, when using the touch command, which would correspond to 0o644. However, POSIX libc implementations use 0o666 inside fopen and then rely on the process-scoped “umask” setting to adjust this number for file creation.