[ 28-Nov-2017 After discussion on the ML, closing as NAD Editorial ]

The standard has a hole in the specification of basic_string's move constructor that seems not only be editorial. In [string.cons] p2:

basic_string(const basic_string& str);
basic_string(basic_string&& str) noexcept;

Effects: Constructs an object of class basic_string as indicated in Table 56. In the second form, str is left in a valid state with an unspecified value.

refers to Table 56, but that table only speaks about copy-ctor. According to Pablo, move and copy differ in what they do. Move ctor of basic_string needs separate table (entry) to describe what happens.