+ * The current() and next() functions only check the current index against the
+ * limit, and previous() only checks the current index against the start,
+ * to see if the iterator already reached the end of the iteration range.
+ *
+ * The assumption - in all iterators - is that the index is moved via the API,
+ * which means it won't go out of bounds, or the index is modified by
+ * user code that knows enough about the iterator implementation to set valid
+ * index values.
+ *