difference_type length(size_type sub = 0) const;
difference_type position(size_type sub = 0) const;
string_type str(size_type sub = 0) const;
const_reference operator[](size_type n) const;
const_reference prefix() const;
const_reference suffix() const;
const_iterator begin() const;
const_iterator cbegin() const;
const_iterator end() const;
const_iterator cend() const;