inequality operator (needed for range-based for)

! @brief compare two value_t enum values @since version 3.0.0 */

post-increment (it++)

subtract from iterator

post-decrement (it--)

! @brief dereference the iterator @pre The iterator is initialized; i.e. `m_object != nullptr`. */

! @brief comparison: less than or equal @pre (1) Both iterators are initialized to point to the same object, or (2) both iterators are value-i

equality operator (needed for InputIterator)

! @brief comparison: greater than @pre (1) Both iterators are initialized to point to the same object, or (2) both iterators are value-initial

! @brief comparison: greater than or equal @pre (1) The iterator is initialized; i.e. `m_object != nullptr`, or (2) both iterators are value-i

! @brief access to successor @pre The iterator is initialized; i.e. `m_object != nullptr`. */