This little bit of snark gave me a laugh: "The red stripe highlights the weekend. For the United States, where week starts on Sunday (but it is anyway considered a part of weekend), alternative frames can be produced."
Can I just say?
Sunday and Saturday are the weekend because they are on each end of the week. If you stack them both up at the back, only Sunday would get to be the weekend. Saturday would just be the day before the end.
A line has got two ends.