Proposed resolution:

This wording is relative to N4606.

1. Change [string.require]/4 as indicated:

   -4- References, pointers, and iterators referring to the elements of a basic_string sequence may be invalidated by the following uses of that basic_string object:

   • as an argument to any standard library function taking a reference to non-const basic_string as an argument.(footnote 230)

   • Calling non-const member functions, except operator[], at, data, front, back, begin, rbegin, end, and rend.