Method GetVisibleRangeIterators

src/widget_type.h:875–881

	 */
	template <typename Tcontainer>
	auto GetVisibleRangeIterators(Tcontainer &container) const
	{
		assert(static_cast<size_t>(this->GetCount()) == container.size()); // Scrollbar and container size must match.
		auto first = std::next(std::begin(container), this->GetPosition());
		auto last = std::next(first, std::min<size_t>(this->GetCapacity(), this->GetCount() - this->GetPosition()));
		return std::make_pair(first, last);
	}

	/**
	 * Return an iterator pointing to the element of a scrolled widget that a user clicked in.