Belloc questions

• What do the words "undefined" mean in bullet point §5.19/2.3 in N4140?
• How to determine if two side effects on a assignment are unsequenced?
• Why does the author emphasizes the fact that operator[] cannot return 0?
• Why the first copy constructor is called in the code below ?
• Trying to understand [class.qual]/2 in the C++ Standard
• Nicolai Josuttis says in his book that the open member function doesn't clear the state flags. That's not what I found in VS2010. Is this a MS issue?
• Is my understanding about [basic.link]/7 in N4140 correct?
• §7.1.6.3/1 (C++14) doesn't accept the construction in the second snippet below. Why is this?
• Why can't a const T*& bind to a T*?
• Why is it that my second snippet below shows undefined behavior?

Belloc answers