diff --git a/sprout/container/container_holder.hpp b/sprout/container/container_holder.hpp
index 146f85dd..2d7997c5 100644
--- a/sprout/container/container_holder.hpp
+++ b/sprout/container/container_holder.hpp
@@ -2,6 +2,7 @@
 #define SPROUT_CONTAINER_CONTAINER_HOLDER_HPP
 
 #include <utility>
+#include <stdexcept>
 #include <sprout/config.hpp>
 #include <sprout/container/traits.hpp>
 #include <sprout/container/functions.hpp>
@@ -82,6 +83,35 @@ namespace sprout {
 		SPROUT_CONSTEXPR const_param_type get_internal() const {
 			return *container;
 		}
+		// element access:
+		reference operator[](size_type i) {
+			return *sprout::next(begin(), i);
+		}
+		SPROUT_CONSTEXPR const_reference operator[](size_type i) const {
+			return *sprout::next(begin(), i);
+		}
+		reference at(size_type i) {
+			return i < size() ? (*this)[i]
+				: (throw std::out_of_range("container_holder<>: index out of range"), (*this)[i])
+				;
+		}
+		SPROUT_CONSTEXPR const_reference at(size_type i) const {
+			return i < size() ? (*this)[i]
+				: (throw std::out_of_range("container_holder<>: index out of range"), (*this)[i])
+				;
+		}
+		reference front() {
+			return *begin();
+		}
+		SPROUT_CONSTEXPR const_reference front() const {
+			return *begin();
+		}
+		reference back() {
+			return *sprout::next(begin(), size() - 1);
+		}
+		SPROUT_CONSTEXPR const_reference back() const {
+			return *sprout::next(begin(), size() - 1);
+		}
 	};
 
 	//
diff --git a/sprout/cstring/memchr.hpp b/sprout/cstring/memchr.hpp
index c9e5e3b5..81ff7976 100644
--- a/sprout/cstring/memchr.hpp
+++ b/sprout/cstring/memchr.hpp
@@ -30,9 +30,9 @@ namespace sprout {
 	inline SPROUT_CONSTEXPR void const*
 	memchr(void const* s, int c, std::size_t n) {
 		return sprout::detail::memchr_impl(
-			sprout::as_iterator_base(
+			sprout::ptr_unindex(
 				sprout::find(
-					sprout::as_iterator(static_cast<unsigned char const*>(s)), sprout::as_iterator(static_cast<unsigned char const*>(s), n),
+					sprout::ptr_index(static_cast<unsigned char const*>(s)), sprout::ptr_index(static_cast<unsigned char const*>(s), n),
 					static_cast<unsigned char>(c)
 					)
 				),
@@ -43,9 +43,9 @@ namespace sprout {
 	inline SPROUT_CONSTEXPR void*
 	memchr(void* s, int c, std::size_t n) {
 		return sprout::detail::memchr_impl(
-			sprout::as_iterator_base(
+			sprout::ptr_unindex(
 				sprout::find(
-					sprout::as_iterator(static_cast<unsigned char*>(s)), sprout::as_iterator(static_cast<unsigned char*>(s), n),
+					sprout::ptr_index(static_cast<unsigned char*>(s)), sprout::ptr_index(static_cast<unsigned char*>(s), n),
 					static_cast<unsigned char>(c)
 					)
 				),
diff --git a/sprout/cstring/memcmp.hpp b/sprout/cstring/memcmp.hpp
index 9cbb4277..dc515505 100644
--- a/sprout/cstring/memcmp.hpp
+++ b/sprout/cstring/memcmp.hpp
@@ -15,8 +15,8 @@ namespace sprout {
 	inline SPROUT_CONSTEXPR int
 	memcmp(void const* s1, void const* s2, std::size_t n) {
 		return sprout::tristate_lexicographical_compare(
-			sprout::as_iterator(static_cast<unsigned char const*>(s1)), sprout::as_iterator(static_cast<unsigned char const*>(s1), n),
-			sprout::as_iterator(static_cast<unsigned char const*>(s2)), sprout::as_iterator(static_cast<unsigned char const*>(s2), n)
+			sprout::ptr_index(static_cast<unsigned char const*>(s1)), sprout::ptr_index(static_cast<unsigned char const*>(s1), n),
+			sprout::ptr_index(static_cast<unsigned char const*>(s2)), sprout::ptr_index(static_cast<unsigned char const*>(s2), n)
 			);
 	}
 }	// namespace sprout
diff --git a/sprout/cstring/strlen.hpp b/sprout/cstring/strlen.hpp
index add8841e..68392c46 100644
--- a/sprout/cstring/strlen.hpp
+++ b/sprout/cstring/strlen.hpp
@@ -70,8 +70,8 @@ namespace sprout {
 	inline SPROUT_CONSTEXPR std::size_t
 	strlen(char const* s, std::size_t n) {
 		return sprout::distance(
-			sprout::as_iterator(s),
-			sprout::find(sprout::as_iterator(s), sprout::as_iterator(s, n), '\0')
+			sprout::ptr_index(s),
+			sprout::find(sprout::ptr_index(s), sprout::ptr_index(s, n), '\0')
 			);
 	}
 
@@ -91,8 +91,8 @@ namespace sprout {
 	strlen(Elem* s, std::size_t n) {
 		typedef typename std::decay<Elem>::type type;
 		return sprout::distance(
-			sprout::as_iterator(s),
-			sprout::find(sprout::as_iterator(s), sprout::as_iterator(s, n), type())
+			sprout::ptr_index(s),
+			sprout::find(sprout::ptr_index(s), sprout::ptr_index(s, n), type())
 			);
 	}
 }	// namespace sprout
diff --git a/sprout/cstring/strncmp.hpp b/sprout/cstring/strncmp.hpp
index e1d4dbdf..5528dddd 100644
--- a/sprout/cstring/strncmp.hpp
+++ b/sprout/cstring/strncmp.hpp
@@ -17,8 +17,8 @@ namespace sprout {
 	inline SPROUT_CONSTEXPR int
 	strncmp(char const* s1, char const* s2, std::size_t n) {
 		return sprout::tristate_lexicographical_compare(
-			sprout::as_iterator(s1), sprout::as_iterator(s1, n), '\0',
-			sprout::as_iterator(s2), sprout::as_iterator(s2, n), '\0'
+			sprout::ptr_index(s1), sprout::ptr_index(s1, n), '\0',
+			sprout::ptr_index(s2), sprout::ptr_index(s2, n), '\0'
 			);
 	}
 
@@ -30,8 +30,8 @@ namespace sprout {
 	strncmp(Elem* s1, Elem* s2, std::size_t n) {
 		typedef typename std::decay<Elem>::type type;
 		return sprout::tristate_lexicographical_compare(
-			sprout::as_iterator(s1), sprout::as_iterator(s1, n), type(),
-			sprout::as_iterator(s2), sprout::as_iterator(s2, n), type()
+			sprout::ptr_index(s1), sprout::ptr_index(s1, n), type(),
+			sprout::ptr_index(s2), sprout::ptr_index(s2, n), type()
 			);
 	}
 }	// namespace sprout
diff --git a/sprout/cwchar/wmemchr.hpp b/sprout/cwchar/wmemchr.hpp
index 8a2ede3e..ab86a60a 100644
--- a/sprout/cwchar/wmemchr.hpp
+++ b/sprout/cwchar/wmemchr.hpp
@@ -31,9 +31,9 @@ namespace sprout {
 	inline SPROUT_CONSTEXPR wchar_t const*
 	wmemchr(wchar_t const* s, wchar_t c, size_t n) {
 		return sprout::detail::wmemchr_impl(
-			sprout::as_iterator_base(
+			sprout::ptr_unindex(
 				sprout::find(
-					sprout::as_iterator(s), sprout::as_iterator(s, n),
+					sprout::ptr_index(s), sprout::ptr_index(s, n),
 					c
 					)
 				),
@@ -44,9 +44,9 @@ namespace sprout {
 	inline SPROUT_CONSTEXPR wchar_t*
 	wmemchr(wchar_t* s, wchar_t c, size_t n) {
 		return sprout::detail::wmemchr_impl(
-			sprout::as_iterator_base(
+			sprout::ptr_unindex(
 				sprout::find(
-					sprout::as_iterator(s), sprout::as_iterator(s, n),
+					sprout::ptr_index(s), sprout::ptr_index(s, n),
 					c
 					)
 				),
diff --git a/sprout/cwchar/wmemcmp.hpp b/sprout/cwchar/wmemcmp.hpp
index edf59495..63beef5a 100644
--- a/sprout/cwchar/wmemcmp.hpp
+++ b/sprout/cwchar/wmemcmp.hpp
@@ -16,8 +16,8 @@ namespace sprout {
 	inline SPROUT_CONSTEXPR int
 	wmemcmp(wchar_t const* s1, wchar_t const* s2, std::size_t n) {
 		return sprout::tristate_lexicographical_compare(
-			sprout::as_iterator(s1), sprout::as_iterator(s1, n),
-			sprout::as_iterator(s2), sprout::as_iterator(s2, n)
+			sprout::ptr_index(s1), sprout::ptr_index(s1, n),
+			sprout::ptr_index(s2), sprout::ptr_index(s2, n)
 			);
 	}
 }	// namespace sprout
diff --git a/sprout/iterator/ptr_index_iterator.hpp b/sprout/iterator/ptr_index_iterator.hpp
index d4375dd7..7397ac91 100644
--- a/sprout/iterator/ptr_index_iterator.hpp
+++ b/sprout/iterator/ptr_index_iterator.hpp
@@ -223,41 +223,41 @@ namespace sprout {
 	}
 
 	//
-	// as_iterator
+	// ptr_index
 	//
 	template<typename T>
 	inline SPROUT_CONSTEXPR sprout::ptr_index_iterator<T>
-	as_iterator(T* p) {
+	ptr_index(T* p) {
 		return sprout::make_ptr_index_iterator(p);
 	}
 	template<typename T>
 	inline SPROUT_CONSTEXPR sprout::ptr_index_iterator<T>
-	as_iterator(T* p, typename std::iterator_traits<T*>::difference_type n) {
+	ptr_index(T* p, typename std::iterator_traits<T*>::difference_type n) {
 		return sprout::make_ptr_index_iterator(p, n);
 	}
 
 	template<typename Iterator>
 	inline SPROUT_CONSTEXPR Iterator
-	as_iterator(Iterator const& it) {
+	ptr_index(Iterator const& it) {
 		return it;
 	}
 	template<typename Iterator>
 	inline SPROUT_CONSTEXPR Iterator
-	as_iterator(Iterator const& it, typename std::iterator_traits<Iterator>::difference_type n) {
+	ptr_index(Iterator const& it, typename std::iterator_traits<Iterator>::difference_type n) {
 		return sprout::next(it, n);
 	}
 
 	//
-	// as_iterator_base
+	// ptr_unindex
 	//
 	template<typename T>
 	inline SPROUT_CONSTEXPR typename sprout::ptr_index_iterator<T>::pointer
-	as_iterator_base(sprout::ptr_index_iterator<T> const& it) {
+	ptr_unindex(sprout::ptr_index_iterator<T> const& it) {
 		return it.ptr();
 	}
 	template<typename Iterator>
 	inline SPROUT_CONSTEXPR Iterator
-	as_iterator_base(Iterator const& it) {
+	ptr_unindex(Iterator const& it) {
 		return it;
 	}
 
diff --git a/sprout/string/char_traits.hpp b/sprout/string/char_traits.hpp
index 2c630de3..757ff6e4 100644
--- a/sprout/string/char_traits.hpp
+++ b/sprout/string/char_traits.hpp
@@ -74,8 +74,8 @@ namespace sprout {
 		}
 		static SPROUT_CONSTEXPR int compare(char_type const* s1, char_type const* s2, std::size_t n) {
 			return sprout::tristate_lexicographical_compare(
-				sprout::as_iterator(s1), sprout::as_iterator(s1, n), char_type(),
-				sprout::as_iterator(s2), sprout::as_iterator(s2, n), char_type(),
+				sprout::ptr_index(s1), sprout::ptr_index(s1, n), char_type(),
+				sprout::ptr_index(s2), sprout::ptr_index(s2, n), char_type(),
 				sprout::detail::char_traits_lt<char_traits>()
 				);
 		}
@@ -84,9 +84,9 @@ namespace sprout {
 		}
 		static SPROUT_CONSTEXPR char_type const* find(char_type const* s, std::size_t n, char_type const& a) {
 			return find_impl(
-				sprout::as_iterator_base(
+				sprout::ptr_unindex(
 					sprout::find_if(
-						sprout::as_iterator(s), sprout::as_iterator(s, n),
+						sprout::ptr_index(s), sprout::ptr_index(s, n),
 						sprout::bind2nd(sprout::detail::char_traits_eq<char_traits>(), a)
 						)
 					),
@@ -121,7 +121,7 @@ namespace sprout {
 		template<typename ConstIterator>
 		static SPROUT_CONSTEXPR int compare(char_type const* s1, ConstIterator s2, std::size_t n) {
 			return sprout::tristate_lexicographical_compare(
-				sprout::as_iterator(s1), sprout::as_iterator(s1, n), char_type(),
+				sprout::ptr_index(s1), sprout::ptr_index(s1, n), char_type(),
 				s2, s2 + n, char_type(),
 				sprout::detail::char_traits_lt<char_traits>()
 				);
@@ -130,7 +130,7 @@ namespace sprout {
 		static SPROUT_CONSTEXPR int compare(ConstIterator s1, char_type const* s2, std::size_t n) {
 			return sprout::tristate_lexicographical_compare(
 				s1, s1 + n, char_type(),
-				sprout::as_iterator(s2), sprout::as_iterator(s2, n), char_type(),
+				sprout::ptr_index(s2), sprout::ptr_index(s2, n), char_type(),
 				sprout::detail::char_traits_lt<char_traits>()
 				);
 		}
@@ -148,7 +148,7 @@ namespace sprout {
 		}
 		template<typename ConstIterator>
 		static SPROUT_CONSTEXPR ConstIterator find(ConstIterator s, std::size_t n, char_type const& a) {
-			return sprout::as_iterator_base(
+			return sprout::ptr_unindex(
 				sprout::find_if(
 					s, s + n,
 					sprout::bind2nd(sprout::detail::char_traits_eq<char_traits>(), a)
@@ -190,9 +190,9 @@ namespace sprout {
 			return sprout::strlen(s, n);
 		}
 		static SPROUT_CONSTEXPR char_type const* find(char_type const* s, std::size_t n, char_type const& a) {
-			return sprout::as_iterator_base(
+			return sprout::ptr_unindex(
 				sprout::find_if(
-					sprout::as_iterator(s), sprout::as_iterator(s, n),
+					sprout::ptr_index(s), sprout::ptr_index(s, n),
 					sprout::bind2nd(sprout::detail::char_traits_eq<traits_type>(), a)
 					)
 				);
diff --git a/sprout/sub_array/sub_array.hpp b/sprout/sub_array/sub_array.hpp
index 625c9e23..f97b5354 100644
--- a/sprout/sub_array/sub_array.hpp
+++ b/sprout/sub_array/sub_array.hpp
@@ -284,14 +284,12 @@ namespace sprout {
 			return *sprout::next(sprout::begin(get_array()), to_first_ + i);
 		}
 		reference at(size_type i) {
-			return i < size()
-				? *sprout::next(sprout::begin(get_array()), to_first_ + i)
+			return i < size() ? *sprout::next(sprout::begin(get_array()), to_first_ + i)
 				: (throw std::out_of_range("sub_array<>: index out of range"), *sprout::next(sprout::begin(get_array()), to_first_ + i))
 				;
 		}
 		SPROUT_CONSTEXPR const_reference at(size_type i) const {
-			return i < size()
-				? *sprout::next(sprout::begin(get_array()), to_first_ + i)
+			return i < size() ? *sprout::next(sprout::begin(get_array()), to_first_ + i)
 				: (throw std::out_of_range("sub_array<>: index out of range"), *sprout::next(sprout::begin(get_array()), to_first_ + i))
 				;
 		}
@@ -359,6 +357,12 @@ namespace sprout {
 		SPROUT_CONSTEXPR difference_type to_last() const {
 			return to_last_;
 		}
+		SPROUT_CONSTEXPR difference_type from_begin() const {
+			return to_first_;
+		}
+		SPROUT_CONSTEXPR difference_type from_end() const {
+			return to_last_ - sprout::size(get_array());
+		}
 	};
 	template<typename Container>
 	SPROUT_CONSTEXPR_OR_CONST typename sprout::sub_array<Container>::size_type sprout::sub_array<Container>::enumerable_size;