Proposed resolution:

This wording is relative to N4659.

1. Edit [string.capacity] as indicated:

   void reserve(size_type res_arg=0);
   

   -10- The member function reserve() is a directive that informs a basic_string object of a planned change in size, so that it can manage the storage allocation accordingly.

   -11- Effects: After reserve(), capacity() is greater or equal to the argument of reserve, if reallocation happens; and equal to the previous value of capacity() otherwise. Reallocation happens at this point if and only if the current capacity is less than the argument of reserve(). [Note: Calling reserve() with a res_arg argument less than capacity() is in effect a non-binding shrink request. A call with res_arg <= size() is in effect a non-binding shrink-to-fit request. — end note]

   -12- Throws: length_error if res_arg > max_size().