diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 10e6c32..990b8e1 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -1,6 +1,6 @@
-## Contributing to the Guideline Support Library
+## Contributing to the Guidelines Support Library
 
-The Guideline Support Library (GSL) contains functions and types that are suggested for use by the
+The Guidelines Support Library (GSL) contains functions and types that are suggested for use by the
 [C++ Core Guidelines](https://github.com/isocpp/CppCoreGuidelines). GSL design changes are made only as a result of modifications to the Guidelines. 
 
 GSL is accepting contributions that improve or refine any of the types in this library as well as ports to other platforms. Changes should have an issue 
diff --git a/README.md b/README.md
index 183553f..df9fcb8 100644
--- a/README.md
+++ b/README.md
@@ -36,6 +36,8 @@ The test suite that exercises GSL has been built and passes successfully on the
 * GNU/Linux using Clang/LLVM 6.0
 * GNU/Linux using Clang/LLVM 7.0
 * GNU/Linux using GCC 5.1
+* OS X Mojave 10.14.4 using Apple LLVM version 10.0.0 (10.0.1.10010046)
+* OS X Mojave 10.14.3 using Apple LLVM version 10.0.0 (clang-1000.11.45.5)
 * OS X Yosemite using Xcode with Apple Clang 7.0.0.7000072
 * OS X Yosemite using GCC-5.2.0
 * OS X Sierra 10.12.4 using Apple LLVM version 8.1.0 (Clang-802.0.42)
diff --git a/ThirdPartyNotices.txt b/ThirdPartyNotices.txt
index 94b9acc..ebf7b6e 100644
--- a/ThirdPartyNotices.txt
+++ b/ThirdPartyNotices.txt
@@ -2,7 +2,7 @@
 THIRD-PARTY SOFTWARE NOTICES AND INFORMATION
 Do Not Translate or Localize
 
-GSL: Guideline Support Library incorporates third party material from the projects listed below. The original copyright notice and the license under which Microsoft received such third party material are set forth below. Microsoft reserves all other rights not expressly granted, whether by implication, estoppel or otherwise.  
+GSL: Guidelines Support Library incorporates third party material from the projects listed below. The original copyright notice and the license under which Microsoft received such third party material are set forth below. Microsoft reserves all other rights not expressly granted, whether by implication, estoppel or otherwise.  
 
 
 1.	Catch (https://github.com/philsquared/Catch)
diff --git a/include/gsl/gsl_util b/include/gsl/gsl_util
index 0fce689..e4b2daa 100644
--- a/include/gsl/gsl_util
+++ b/include/gsl/gsl_util
@@ -24,7 +24,7 @@
 #include <exception>        // for exception
 #include <initializer_list> // for initializer_list
 #include <type_traits>      // for is_signed, integral_constant
-#include <utility>          // for forward
+#include <utility>          // for exchange, forward
 
 #if defined(_MSC_VER) && !defined(__clang__)
 
@@ -59,10 +59,7 @@ class final_action
 public:
     explicit final_action(F f) noexcept : f_(std::move(f)) {}
 
-    final_action(final_action&& other) noexcept : f_(std::move(other.f_)), invoke_(other.invoke_)
-    {
-        other.invoke_ = false;
-    }
+    final_action(final_action&& other) noexcept : f_(std::move(other.f_)), invoke_(std::exchange(other.invoke_, false)) {}
 
     final_action(const final_action&) = delete;
     final_action& operator=(const final_action&) = delete;
diff --git a/include/gsl/multi_span b/include/gsl/multi_span
index 0c1506e..3a2d982 100644
--- a/include/gsl/multi_span
+++ b/include/gsl/multi_span
@@ -23,7 +23,6 @@
 
 #include <algorithm> // for transform, lexicographical_compare
 #include <array>     // for array
-#include <cassert>
 #include <cstddef>          // for ptrdiff_t, size_t, nullptr_t
 #include <cstdint>          // for PTRDIFF_MAX
 #include <functional>       // for divides, multiplies, minus, negate, plus
@@ -49,13 +48,19 @@
 #pragma warning(disable : 26473) // in some instantiations we cast to the same type
 #pragma warning(disable : 26490) // TODO: bug in parser - attributes and templates
 #pragma warning(disable : 26465) // TODO: bug - suppression does not work on template functions
+#pragma warning(disable : 4996)  // use of function or classes marked [[deprecated]]
 
 #if _MSC_VER < 1910
 #pragma push_macro("constexpr")
 #define constexpr /*constexpr*/
 
-#endif                          // _MSC_VER < 1910
-#endif                          // _MSC_VER
+#endif // _MSC_VER < 1910
+#endif // _MSC_VER
+
+#if __clang__ || __GNUC__
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
+#endif
 
 // GCC 7 does not like the signed unsigned missmatch (size_t ptrdiff_t)
 // While there is a conversion from signed to unsigned, it happens at
@@ -76,18 +81,18 @@ namespace gsl
 namespace details
 {
     template <typename SizeType>
-    struct SizeTypeTraits
+    struct [[deprecated]] SizeTypeTraits
     {
         static const SizeType max_value = std::numeric_limits<SizeType>::max();
     };
 
     template <typename... Ts>
-    class are_integral : public std::integral_constant<bool, true>
+    class [[deprecated]] are_integral : public std::integral_constant<bool, true>
     {
     };
 
     template <typename T, typename... Ts>
-    class are_integral<T, Ts...>
+    class [[deprecated]] are_integral<T, Ts...>
         : public std::integral_constant<bool,
                                         std::is_integral<T>::value && are_integral<Ts...>::value>
     {
@@ -95,8 +100,7 @@ namespace details
 } // namespace details
 
 template <std::size_t Rank>
-class multi_span_index final
-{
+class [[deprecated]] multi_span_index final {
     static_assert(Rank > 0, "Rank must be greater than 0!");
 
     template <std::size_t OtherRank>
@@ -111,7 +115,7 @@ public:
 
     constexpr multi_span_index() noexcept {}
 
-    constexpr multi_span_index(const value_type (&values)[Rank]) noexcept
+    constexpr multi_span_index(const value_type(&values)[Rank]) noexcept
     {
         GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
         GSL_SUPPRESS(bounds.3) // NO-FORMAT: attribute
@@ -139,7 +143,7 @@ public:
     // Preconditions: component_idx < rank
     GSL_SUPPRESS(bounds.2) // NO-FORMAT: attribute
     GSL_SUPPRESS(bounds.4) // NO-FORMAT: attribute
-    constexpr const_reference operator[](std::size_t component_idx) const 
+    constexpr const_reference operator[](std::size_t component_idx) const
     {
         Expects(component_idx < Rank); // Component index must be less than rank
         return elems[component_idx];
@@ -152,10 +156,7 @@ public:
         return std::equal(elems, elems + rank, rhs.elems);
     }
 
-    constexpr bool operator!=(const multi_span_index& rhs) const
-    {
-        return !(*this == rhs);
-    }
+    constexpr bool operator!=(const multi_span_index& rhs) const { return !(*this == rhs); }
 
     constexpr multi_span_index operator+() const noexcept { return *this; }
 
@@ -184,8 +185,7 @@ public:
     {
         GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
         GSL_SUPPRESS(bounds.3) // NO-FORMAT: attribute
-        std::transform(elems, elems + rank, rhs.elems, elems,
-                       std::plus<value_type>{});
+        std::transform(elems, elems + rank, rhs.elems, elems, std::plus<value_type>{});
         return *this;
     }
 
@@ -240,7 +240,7 @@ private:
 
 #if !defined(_MSC_VER) || _MSC_VER >= 1910
 
-struct static_bounds_dynamic_range_t
+struct [[deprecated]] static_bounds_dynamic_range_t
 {
     template <typename T, typename = std::enable_if_t<std::is_integral<T>::value>>
     constexpr operator T() const noexcept
@@ -288,25 +288,22 @@ constexpr static_bounds_dynamic_range_t dynamic_range{};
 const std::ptrdiff_t dynamic_range = -1;
 #endif
 
-struct generalized_mapping_tag
-{
-};
-struct contiguous_mapping_tag : generalized_mapping_tag
+struct [[deprecated]] generalized_mapping_tag
 {
 };
+struct[[deprecated]] contiguous_mapping_tag : generalized_mapping_tag{};
 
 namespace details
 {
 
     template <std::ptrdiff_t Left, std::ptrdiff_t Right>
-    struct LessThan
+    struct [[deprecated]] LessThan
     {
         static const bool value = Left < Right;
     };
 
     template <std::ptrdiff_t... Ranges>
-    struct BoundsRanges
-    {
+    struct [[deprecated]] BoundsRanges {
         using size_type = std::ptrdiff_t;
         static const size_type Depth = 0;
         static const size_type DynamicNum = 0;
@@ -345,7 +342,7 @@ namespace details
     };
 
     template <std::ptrdiff_t... RestRanges>
-    struct BoundsRanges<dynamic_range, RestRanges...> : BoundsRanges<RestRanges...>
+    struct[[deprecated]] BoundsRanges<dynamic_range, RestRanges...> : BoundsRanges<RestRanges...>
     {
         using Base = BoundsRanges<RestRanges...>;
         using size_type = std::ptrdiff_t;
@@ -358,8 +355,9 @@ namespace details
         size_type m_bound;
 
     public:
-        GSL_SUPPRESS(f.23) // NO-FORMAT: attribute // this pointer type is cannot be assigned nullptr - issue in not_null
-        GSL_SUPPRESS(bounds.1)  // NO-FORMAT: attribute
+        GSL_SUPPRESS(
+            f.23) // NO-FORMAT: attribute // this pointer type is cannot be assigned nullptr - issue in not_null
+        GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
         constexpr BoundsRanges(const std::ptrdiff_t* const arr)
             : Base(arr + 1), m_bound(*arr * this->Base::totalSize())
         {
@@ -370,13 +368,13 @@ namespace details
 
         template <std::ptrdiff_t OtherRange, std::ptrdiff_t... RestOtherRanges>
         constexpr BoundsRanges(const BoundsRanges<OtherRange, RestOtherRanges...>& other,
-                     bool /* firstLevel */ = true)
+                               bool /* firstLevel */ = true)
             : Base(static_cast<const BoundsRanges<RestOtherRanges...>&>(other), false)
             , m_bound(other.totalSize())
         {}
 
         template <typename T, std::size_t Dim = 0>
-        constexpr void serialize(T& arr) const
+        constexpr void serialize(T & arr) const
         {
             arr[Dim] = elementNum();
             this->Base::template serialize<T, Dim + 1>(arr);
@@ -400,19 +398,19 @@ namespace details
             return cur < m_bound ? cur + last : -1;
         }
 
-        GSL_SUPPRESS(c.128) // NO-FORMAT: attribute // no pointers to BoundsRanges should be ever used
-        constexpr size_type totalSize() const noexcept
-        {
-            return m_bound;
-        }
+        GSL_SUPPRESS(
+            c.128) // NO-FORMAT: attribute // no pointers to BoundsRanges should be ever used
+        constexpr size_type totalSize() const noexcept { return m_bound; }
 
-        GSL_SUPPRESS(c.128) // NO-FORMAT: attribute // no pointers to BoundsRanges should be ever used
+        GSL_SUPPRESS(
+            c.128) // NO-FORMAT: attribute // no pointers to BoundsRanges should be ever used
         constexpr size_type elementNum() const noexcept
         {
             return totalSize() / this->Base::totalSize();
         }
 
-        GSL_SUPPRESS(c.128) // NO-FORMAT: attribute // no pointers to BoundsRanges should be ever used
+        GSL_SUPPRESS(
+            c.128) // NO-FORMAT: attribute // no pointers to BoundsRanges should be ever used
         constexpr size_type elementNum(std::size_t dim) const noexcept
         {
             if (dim > 0)
@@ -429,7 +427,7 @@ namespace details
     };
 
     template <std::ptrdiff_t CurRange, std::ptrdiff_t... RestRanges>
-    struct BoundsRanges<CurRange, RestRanges...> : BoundsRanges<RestRanges...>
+    struct[[deprecated]] BoundsRanges<CurRange, RestRanges...> : BoundsRanges<RestRanges...>
     {
         using Base = BoundsRanges<RestRanges...>;
         using size_type = std::ptrdiff_t;
@@ -444,7 +442,7 @@ namespace details
 
         template <std::ptrdiff_t OtherRange, std::ptrdiff_t... RestOtherRanges>
         constexpr BoundsRanges(const BoundsRanges<OtherRange, RestOtherRanges...>& other,
-                     bool firstLevel = true)
+                               bool firstLevel = true)
             : Base(static_cast<const BoundsRanges<RestOtherRanges...>&>(other), false)
         {
             GSL_SUPPRESS(type.4) // NO-FORMAT: attribute // TODO: false positive
@@ -452,7 +450,7 @@ namespace details
         }
 
         template <typename T, std::size_t Dim = 0>
-        constexpr void serialize(T& arr) const
+        constexpr void serialize(T & arr) const
         {
             arr[Dim] = elementNum();
             this->Base::template serialize<T, Dim + 1>(arr);
@@ -461,12 +459,11 @@ namespace details
         template <typename T, std::size_t Dim = 0>
         constexpr size_type linearize(const T& arr) const
         {
-            GSL_SUPPRESS(bounds.4) // NO-FORMAT: attribute
+            GSL_SUPPRESS(bounds.4)                            // NO-FORMAT: attribute
             Expects(arr[Dim] >= 0 && arr[Dim] < CurrentRange); // Index is out of range
-            GSL_SUPPRESS(bounds.4) // NO-FORMAT: attribute
+            GSL_SUPPRESS(bounds.4)                            // NO-FORMAT: attribute
             const ptrdiff_t d = arr[Dim];
-            return this->Base::totalSize() * d +
-                   this->Base::template linearize<T, Dim + 1>(arr);
+            return this->Base::totalSize() * d + this->Base::template linearize<T, Dim + 1>(arr);
         }
 
         template <typename T, std::size_t Dim = 0>
@@ -478,19 +475,19 @@ namespace details
             return this->Base::totalSize() * arr[Dim] + last;
         }
 
-        GSL_SUPPRESS(c.128) // NO-FORMAT: attribute // no pointers to BoundsRanges should be ever used
+        GSL_SUPPRESS(
+            c.128) // NO-FORMAT: attribute // no pointers to BoundsRanges should be ever used
         constexpr size_type totalSize() const noexcept
         {
             return CurrentRange * this->Base::totalSize();
         }
 
-        GSL_SUPPRESS(c.128) // NO-FORMAT: attribute // no pointers to BoundsRanges should be ever used
-        constexpr size_type elementNum() const noexcept
-        {
-            return CurrentRange;
-        }
+        GSL_SUPPRESS(
+            c.128) // NO-FORMAT: attribute // no pointers to BoundsRanges should be ever used
+        constexpr size_type elementNum() const noexcept { return CurrentRange; }
 
-        GSL_SUPPRESS(c.128) // NO-FORMAT: attribute // no pointers to BoundsRanges should be ever used
+        GSL_SUPPRESS(
+            c.128) // NO-FORMAT: attribute // no pointers to BoundsRanges should be ever used
         constexpr size_type elementNum(std::size_t dim) const noexcept
         {
             if (dim > 0)
@@ -506,17 +503,14 @@ namespace details
     };
 
     template <typename SourceType, typename TargetType>
-    struct BoundsRangeConvertible
+    struct[[deprecated]] BoundsRangeConvertible
         : public std::integral_constant<bool, (SourceType::TotalSize >= TargetType::TotalSize ||
                                                TargetType::TotalSize == dynamic_range ||
                                                SourceType::TotalSize == dynamic_range ||
-                                               TargetType::TotalSize == 0)>
-    {
-    };
+                                               TargetType::TotalSize == 0)>{};
 
     template <typename TypeChain>
-    struct TypeListIndexer
-    {
+    struct [[deprecated]] TypeListIndexer {
         const TypeChain& obj_;
         constexpr TypeListIndexer(const TypeChain& obj) : obj_(obj) {}
 
@@ -529,13 +523,13 @@ namespace details
         template <std::size_t N, typename MyChain = TypeChain,
                   typename MyBase = typename MyChain::Base>
         constexpr auto getObj(std::false_type)
-            -> decltype(TypeListIndexer<MyBase>(static_cast<const MyBase&>(obj_)).template get<N>())
+            ->decltype(TypeListIndexer<MyBase>(static_cast<const MyBase&>(obj_)).template get<N>())
         {
             return TypeListIndexer<MyBase>(static_cast<const MyBase&>(obj_)).template get<N>();
         }
 
         template <std::size_t N>
-        constexpr auto get() -> decltype(getObj<N - 1>(std::integral_constant<bool, N == 0>()))
+        constexpr auto get()->decltype(getObj<N - 1>(std::integral_constant<bool, N == 0>()))
         {
             return getObj<N - 1>(std::integral_constant<bool, N == 0>());
         }
@@ -555,24 +549,23 @@ namespace details
         for (std::size_t i = 0; i < Rank - 1; ++i)
         {
             GSL_SUPPRESS(bounds.4) // NO-FORMAT: attribute
-                ret[i] = other[i + 1];
+            ret[i] = other[i + 1];
         }
         return ret;
     }
 } // namespace details
 
 template <typename IndexType>
-class bounds_iterator;
+class [[deprecated]] bounds_iterator;
 
 template <std::ptrdiff_t... Ranges>
-class static_bounds
-{
+class [[deprecated]] static_bounds {
 public:
     static_bounds(const details::BoundsRanges<Ranges...>&) {}
 };
 
 template <std::ptrdiff_t FirstRange, std::ptrdiff_t... RestRanges>
-class static_bounds<FirstRange, RestRanges...>
+class[[deprecated]] static_bounds<FirstRange, RestRanges...>
 {
     using MyRanges = details::BoundsRanges<FirstRange, RestRanges...>;
 
@@ -604,10 +597,10 @@ public:
     template <std::size_t Rank, typename SourceType, typename TargetType,
               typename Ret = BoundsRangeConvertible2<typename SourceType::Base,
                                                      typename TargetType::Base, Rank>>
-    static auto helpBoundsRangeConvertible(SourceType, TargetType, std::true_type) -> Ret;
+    static auto helpBoundsRangeConvertible(SourceType, TargetType, std::true_type)->Ret;
 
     template <std::size_t Rank, typename SourceType, typename TargetType>
-    static auto helpBoundsRangeConvertible(SourceType, TargetType, ...) -> std::false_type;
+    static auto helpBoundsRangeConvertible(SourceType, TargetType, ...)->std::false_type;
 
     template <typename SourceType, typename TargetType, std::size_t Rank>
     struct BoundsRangeConvertible2
@@ -724,10 +717,7 @@ public:
         return !(*this == rhs);
     }
 
-    constexpr const_iterator begin() const noexcept
-    {
-        return const_iterator(*this, index_type{});
-    }
+    constexpr const_iterator begin() const noexcept { return const_iterator(*this, index_type{}); }
 
     constexpr const_iterator end() const noexcept
     {
@@ -736,7 +726,7 @@ public:
 };
 
 template <std::size_t Rank>
-class strided_bounds {
+class [[deprecated]] strided_bounds {
     template <std::size_t OtherRank>
     friend class strided_bounds;
 
@@ -760,14 +750,13 @@ public:
 
     constexpr strided_bounds& operator=(const strided_bounds&) noexcept = default;
 
-    constexpr strided_bounds(const value_type (&values)[rank], index_type strides)
+    constexpr strided_bounds(const value_type(&values)[rank], index_type strides)
         : m_extents(values), m_strides(std::move(strides))
     {}
 
     constexpr strided_bounds(const index_type& extents, const index_type& strides) noexcept
         : m_extents(extents), m_strides(strides)
-    {
-    }
+    {}
 
     constexpr index_type strides() const noexcept { return m_strides; }
 
@@ -839,21 +828,14 @@ private:
 };
 
 template <typename T>
-struct is_bounds : std::integral_constant<bool, false>
-{
-};
+struct[[deprecated]] is_bounds : std::integral_constant<bool, false>{};
 template <std::ptrdiff_t... Ranges>
-struct is_bounds<static_bounds<Ranges...>> : std::integral_constant<bool, true>
-{
-};
+struct[[deprecated]] is_bounds<static_bounds<Ranges...>> : std::integral_constant<bool, true>{};
 template <std::size_t Rank>
-struct is_bounds<strided_bounds<Rank>> : std::integral_constant<bool, true>
-{
-};
+struct[[deprecated]] is_bounds<strided_bounds<Rank>> : std::integral_constant<bool, true>{};
 
 template <typename IndexType>
-class bounds_iterator
-{
+class [[deprecated]] bounds_iterator {
 public:
     static const std::size_t rank = IndexType::rank;
     using iterator_category = std::random_access_iterator_tag;
@@ -974,7 +956,6 @@ public:
         return curr_ == rhs.curr_;
     }
 
-
     constexpr bool operator!=(const bounds_iterator& rhs) const noexcept { return !(*this == rhs); }
 
     constexpr bool operator<(const bounds_iterator& rhs) const noexcept
@@ -988,16 +969,15 @@ public:
 
     constexpr bool operator>=(const bounds_iterator& rhs) const noexcept { return !(rhs > *this); }
 
-    void swap(bounds_iterator& rhs) noexcept
+    void swap(bounds_iterator & rhs) noexcept
     {
         std::swap(boundary_, rhs.boundary_);
         std::swap(curr_, rhs.curr_);
     }
 
 private:
-
     GSL_SUPPRESS(bounds.4) // NO-FORMAT: attribute
-    constexpr bool less(index_type& one, index_type& other) const noexcept
+    constexpr bool less(index_type & one, index_type & other) const noexcept
     {
         for (std::size_t i = 0; i < rank; ++i)
         {
@@ -1092,17 +1072,17 @@ namespace details
 } // namespace details
 
 template <typename Span>
-class contiguous_span_iterator;
+class [[deprecated]] contiguous_span_iterator;
 template <typename Span>
-class general_span_iterator;
+class [[deprecated]] general_span_iterator;
 
 template <std::ptrdiff_t DimSize = dynamic_range>
-struct dim_t
+struct [[deprecated]] dim_t
 {
     static const std::ptrdiff_t value = DimSize;
 };
 template <>
-struct dim_t<dynamic_range>
+struct [[deprecated]] dim_t<dynamic_range>
 {
     static const std::ptrdiff_t value = dynamic_range;
     const std::ptrdiff_t dvalue;
@@ -1123,28 +1103,30 @@ constexpr dim_t<N> dim(std::ptrdiff_t n) noexcept
 
 template <typename ValueType, std::ptrdiff_t FirstDimension = dynamic_range,
           std::ptrdiff_t... RestDimensions>
-class multi_span;
+class [[deprecated("gsl::multi_span is deprecated because it is not in the C++ Core Guidelines")]] multi_span;
+
 template <typename ValueType, std::size_t Rank>
-class strided_span;
+class [[deprecated("gsl::strided_span is deprecated because it is not in the C++ Core Guidelines")]] strided_span;
 
 namespace details
 {
     template <typename T, typename = std::true_type>
-    struct SpanTypeTraits
+    struct [[deprecated]] SpanTypeTraits
     {
         using value_type = T;
         using size_type = std::size_t;
     };
 
     template <typename Traits>
-    struct SpanTypeTraits<Traits, typename std::is_reference<typename Traits::span_traits&>::type>
+    struct [[deprecated]] SpanTypeTraits<
+        Traits, typename std::is_reference<typename Traits::span_traits&>::type>
     {
         using value_type = typename Traits::span_traits::value_type;
         using size_type = typename Traits::span_traits::size_type;
     };
 
     template <typename T, std::ptrdiff_t... Ranks>
-    struct SpanArrayTraits
+    struct [[deprecated]] SpanArrayTraits
     {
         using type = multi_span<T, Ranks...>;
         using value_type = T;
@@ -1153,7 +1135,7 @@ namespace details
         using reference = T&;
     };
     template <typename T, std::ptrdiff_t N, std::ptrdiff_t... Ranks>
-    struct SpanArrayTraits<T[N], Ranks...> : SpanArrayTraits<T, Ranks..., N>
+    struct [[deprecated]] SpanArrayTraits<T[N], Ranks...> : SpanArrayTraits<T, Ranks..., N>
     {
     };
 
@@ -1177,7 +1159,7 @@ namespace details
             totalSize, std::integral_constant<bool, BoundsType::dynamic_rank == 1>());
     }
 
-    struct Sep
+    struct [[deprecated]] Sep
     {
     };
 
@@ -1200,36 +1182,35 @@ namespace details
     }
 
     template <typename... Dimensions>
-    struct static_as_multi_span_static_bounds_helper
+    struct [[deprecated]] static_as_multi_span_static_bounds_helper
     {
         using type = static_bounds<(Dimensions::value)...>;
     };
 
     template <typename T>
-    struct is_multi_span_oracle : std::false_type
+    struct [[deprecated]] is_multi_span_oracle : std::false_type
     {
     };
 
     template <typename ValueType, std::ptrdiff_t FirstDimension, std::ptrdiff_t... RestDimensions>
-    struct is_multi_span_oracle<multi_span<ValueType, FirstDimension, RestDimensions...>>
+    struct [[deprecated]] is_multi_span_oracle<multi_span<ValueType, FirstDimension, RestDimensions...>>
         : std::true_type
     {
     };
 
     template <typename ValueType, std::ptrdiff_t Rank>
-    struct is_multi_span_oracle<strided_span<ValueType, Rank>> : std::true_type
+    struct [[deprecated]] is_multi_span_oracle<strided_span<ValueType, Rank>> : std::true_type
     {
     };
 
     template <typename T>
-    struct is_multi_span : is_multi_span_oracle<std::remove_cv_t<T>>
+    struct [[deprecated]] is_multi_span : is_multi_span_oracle<std::remove_cv_t<T>>
     {
     };
 } // namespace details
 
 template <typename ValueType, std::ptrdiff_t FirstDimension, std::ptrdiff_t... RestDimensions>
-class multi_span
-{
+class [[deprecated("gsl::multi_span is deprecated because it is not in the C++ Core Guidelines")]] multi_span {
     // TODO do we still need this?
     template <typename ValueType2, std::ptrdiff_t FirstDimension2,
               std::ptrdiff_t... RestDimensions2>
@@ -1262,8 +1243,7 @@ private:
 public:
     // default constructor - same as constructing from nullptr_t
     GSL_SUPPRESS(type.6) // NO-FORMAT: attribute // TODO: false positive
-    constexpr multi_span() noexcept
-        : multi_span(nullptr, bounds_type{})
+    constexpr multi_span() noexcept : multi_span(nullptr, bounds_type{})
     {
         static_assert(bounds_type::dynamic_rank != 0 ||
                           (bounds_type::dynamic_rank == 0 && bounds_type::static_size == 0),
@@ -1273,8 +1253,7 @@ public:
 
     // construct from nullptr - get an empty multi_span
     GSL_SUPPRESS(type.6) // NO-FORMAT: attribute // TODO: false positive
-    constexpr multi_span(std::nullptr_t) noexcept
-        : multi_span(nullptr, bounds_type{})
+    constexpr multi_span(std::nullptr_t) noexcept : multi_span(nullptr, bounds_type{})
     {
         static_assert(bounds_type::dynamic_rank != 0 ||
                           (bounds_type::dynamic_rank == 0 && bounds_type::static_size == 0),
@@ -1298,8 +1277,7 @@ public:
     // construct from a single element
 
     GSL_SUPPRESS(type.6) // NO-FORMAT: attribute // TODO: false positive
-    constexpr multi_span(reference data) noexcept
-        : multi_span(&data, bounds_type{1})
+    constexpr multi_span(reference data) noexcept : multi_span(&data, bounds_type{1})
     {
         static_assert(bounds_type::dynamic_rank > 0 || bounds_type::static_size == 0 ||
                           bounds_type::static_size == 1,
@@ -1308,17 +1286,14 @@ public:
     }
 
     // prevent constructing from temporaries for single-elements
-    constexpr multi_span(value_type&&) = delete;
+    constexpr multi_span(value_type &&) = delete;
 
     // construct from pointer + length
     GSL_SUPPRESS(type.6) // NO-FORMAT: attribute // TODO: false positive
-    constexpr multi_span(pointer ptr, size_type size)
-        : multi_span(ptr, bounds_type{size})
-    {}
+    constexpr multi_span(pointer ptr, size_type size) : multi_span(ptr, bounds_type{size}) {}
 
     // construct from pointer + length - multidimensional
-    constexpr multi_span(pointer data, bounds_type bounds)
-        : data_(data), bounds_(std::move(bounds))
+    constexpr multi_span(pointer data, bounds_type bounds) : data_(data), bounds_(std::move(bounds))
     {
         Expects((bounds_.size() > 0 && data != nullptr) || bounds_.size() == 0);
     }
@@ -1336,7 +1311,7 @@ public:
 
     // construct from n-dimensions static array
     template <typename T, std::size_t N, typename Helper = details::SpanArrayTraits<T, N>>
-    constexpr multi_span(T (&arr)[N])
+    constexpr multi_span(T(&arr)[N])
         : multi_span(reinterpret_cast<pointer>(arr), bounds_type{typename Helper::bounds_type{}})
     {
         static_assert(std::is_convertible<typename Helper::value_type(*)[], value_type(*)[]>::value,
@@ -1357,7 +1332,7 @@ public:
 
     // construct from std::array
     template <typename T, std::size_t N>
-    constexpr multi_span(std::array<T, N>& arr)
+    constexpr multi_span(std::array<T, N> & arr)
         : multi_span(arr.data(), bounds_type{static_bounds<N>{}})
     {
         static_assert(
@@ -1381,7 +1356,7 @@ public:
 
     // prevent constructing from temporary std::array
     template <typename T, std::size_t N>
-    constexpr multi_span(std::array<T, N>&& arr) = delete;
+    constexpr multi_span(std::array<T, N> && arr) = delete;
 
     // construct from containers
     // future: could use contiguous_iterator_traits to identify only contiguous containers
@@ -1389,11 +1364,11 @@ public:
     template <typename Cont, typename DataType = typename Cont::value_type,
               typename = std::enable_if_t<
                   !details::is_multi_span<Cont>::value &&
-                  std::is_convertible<DataType (*)[], value_type (*)[]>::value &&
+                  std::is_convertible<DataType(*)[], value_type(*)[]>::value &&
                   std::is_same<std::decay_t<decltype(std::declval<Cont>().size(),
                                                      *std::declval<Cont>().data())>,
                                DataType>::value>>
-    constexpr multi_span(Cont& cont)
+    constexpr multi_span(Cont & cont)
         : multi_span(static_cast<pointer>(cont.data()),
                      details::newBoundsHelper<bounds_type>(narrow_cast<size_type>(cont.size())))
     {}
@@ -1402,11 +1377,11 @@ public:
     template <typename Cont, typename DataType = typename Cont::value_type,
               typename = std::enable_if_t<
                   !details::is_multi_span<Cont>::value &&
-                  std::is_convertible<DataType (*)[], value_type (*)[]>::value &&
+                  std::is_convertible<DataType(*)[], value_type(*)[]>::value &&
                   std::is_same<std::decay_t<decltype(std::declval<Cont>().size(),
                                                      *std::declval<Cont>().data())>,
                                DataType>::value>>
-    explicit constexpr multi_span(Cont&& cont) = delete;
+    explicit constexpr multi_span(Cont && cont) = delete;
 
     // construct from a convertible multi_span
     template <typename OtherValueType, std::ptrdiff_t... OtherDimensions,
@@ -1419,7 +1394,7 @@ public:
 
     // trivial copy and move
     constexpr multi_span(const multi_span&) = default;
-    constexpr multi_span(multi_span&&) = default;
+    constexpr multi_span(multi_span &&) = default;
 
     // trivial assignment
     constexpr multi_span& operator=(const multi_span&) = default;
@@ -1493,8 +1468,7 @@ public:
     }
 
     // section - creates a non-contiguous, strided multi_span from a contiguous one
-    constexpr strided_span<ValueType, Rank> section(index_type origin,
-                                                    index_type extents) const
+    constexpr strided_span<ValueType, Rank> section(index_type origin, index_type extents) const
     {
         const size_type size = this->bounds().total_size() - this->bounds().linearize(origin);
         return {&this->operator[](origin), size,
@@ -1636,8 +1610,8 @@ public:
     template <typename OtherValueType, std::ptrdiff_t... OtherDimensions,
               typename = std::enable_if_t<std::is_same<std::remove_cv_t<value_type>,
                                                        std::remove_cv_t<OtherValueType>>::value>>
-    constexpr bool operator>(const multi_span<OtherValueType, OtherDimensions...>& other) const
-        noexcept
+    constexpr bool operator>(const multi_span<OtherValueType, OtherDimensions...>& other)
+        const noexcept
     {
         return (other < *this);
     }
@@ -1673,7 +1647,8 @@ constexpr auto as_multi_span(SpanType s, Dimensions2... dims)
 
 // convert a multi_span<T> to a multi_span<const byte>
 template <typename U, std::ptrdiff_t... Dimensions>
-multi_span<const byte, dynamic_range> as_bytes(multi_span<U, Dimensions...> s) noexcept
+multi_span<const byte, dynamic_range>
+as_bytes(multi_span<U, Dimensions...> s) noexcept
 {
     static_assert(std::is_trivial<std::decay_t<U>>::value,
                   "The value_type of multi_span must be a trivial type.");
@@ -1759,7 +1734,8 @@ constexpr auto as_multi_span(T* arr, std::ptrdiff_t len) ->
 }
 
 template <typename T, std::size_t N>
-constexpr auto as_multi_span(T (&arr)[N]) -> typename details::SpanArrayTraits<T, N>::type
+constexpr auto as_multi_span(T (&arr)[N]) ->
+    typename details::SpanArrayTraits<T, N>::type
 {
     return {arr};
 }
@@ -1812,7 +1788,7 @@ constexpr auto as_multi_span(std::basic_string<CharT, Traits, Allocator>& str)
 // strided_span is an extension that is not strictly part of the GSL at this time.
 // It is kept here while the multidimensional interface is still being defined.
 template <typename ValueType, std::size_t Rank>
-class strided_span
+class [[deprecated("gsl::strided_span is deprecated because it is not in the C++ Core Guidelines")]] strided_span
 {
 public:
     using bounds_type = strided_bounds<Rank>;
@@ -2055,8 +2031,7 @@ private:
 };
 
 template <class Span>
-class contiguous_span_iterator
-{
+class [[deprecated]] contiguous_span_iterator {
 public:
     using iterator_category = std::random_access_iterator_tag;
     using value_type = typename Span::value_type;
@@ -2072,7 +2047,8 @@ private:
     const Span* m_validator;
 
     GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
-    void validateThis() const {
+    void validateThis() const
+    {
         // iterator is out of range of the array
         Expects(data_ >= m_validator->data_ && data_ < m_validator->data_ + m_validator->size());
     }
@@ -2161,7 +2137,7 @@ public:
     bool operator>(const contiguous_span_iterator& rhs) const { return rhs < *this; }
     bool operator>=(const contiguous_span_iterator& rhs) const { return !(rhs > *this); }
 
-    void swap(contiguous_span_iterator& rhs) noexcept
+    void swap(contiguous_span_iterator & rhs) noexcept
     {
         std::swap(data_, rhs.data_);
         std::swap(m_validator, rhs.m_validator);
@@ -2176,7 +2152,7 @@ contiguous_span_iterator<Span> operator+(typename contiguous_span_iterator<Span>
 }
 
 template <typename Span>
-class general_span_iterator {
+class [[deprecated]] general_span_iterator {
 public:
     using iterator_category = std::random_access_iterator_tag;
     using value_type = typename Span::value_type;
@@ -2259,7 +2235,7 @@ public:
     bool operator<=(const general_span_iterator& rhs) const { return !(rhs < *this); }
     bool operator>(const general_span_iterator& rhs) const { return rhs < *this; }
     bool operator>=(const general_span_iterator& rhs) const { return !(rhs > *this); }
-    void swap(general_span_iterator& rhs) noexcept
+    void swap(general_span_iterator & rhs) noexcept
     {
         std::swap(m_itr, rhs.m_itr);
         std::swap(m_container, rhs.m_container);
@@ -2290,4 +2266,8 @@ general_span_iterator<Span> operator+(typename general_span_iterator<Span>::diff
 #pragma GCC diagnostic pop
 #endif // __GNUC__ > 6
 
+#if __clang__ || __GNUC__
+#pragma GCC diagnostic pop
+#endif
+
 #endif // GSL_MULTI_SPAN_H
diff --git a/include/gsl/pointers b/include/gsl/pointers
index 0f2987a..7373826 100644
--- a/include/gsl/pointers
+++ b/include/gsl/pointers
@@ -197,7 +197,7 @@ namespace gsl
 //
 // Restricts a pointer or smart pointer to only hold non-null values,
 //
-// - provides a strict (i.e. explicit contructor from T) wrapper of not_null
+// - provides a strict (i.e. explicit constructor from T) wrapper of not_null
 // - to be used for new code that wishes the design to be cleaner and make not_null
 //   checks intentional, or in old code that would like to make the transition.
 //
@@ -205,9 +205,9 @@ namespace gsl
 //   by strict_not_null and fix compilation errors
 //
 //   Expect to
-//   - remove all unneded conversions from raw pointer to not_null and back
-//   - make API clear by specifyning not_null in parameters where needed
-//   - remove unnesessary asserts
+//   - remove all unneeded conversions from raw pointer to not_null and back
+//   - make API clear by specifying not_null in parameters where needed
+//   - remove unnecessary asserts
 //
 template <class T>
 class strict_not_null: public not_null<T>
diff --git a/tests/bounds_tests.cpp b/tests/bounds_tests.cpp
index e586d44..d72e31a 100644
--- a/tests/bounds_tests.cpp
+++ b/tests/bounds_tests.cpp
@@ -18,6 +18,12 @@
 // blanket turn off warnings from CppCoreCheck from catch
 // so people aren't annoyed by them when running the tool.
 #pragma warning(disable : 26440 26426) // from catch
+#pragma warning(disable : 4996)  // use of function or classes marked [[deprecated]]
+#endif
+
+#if __clang__ || __GNUC__
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
 #endif
 
 #include <catch/catch.hpp> // for AssertionHandler, StringRef, TEST_CASE
@@ -113,3 +119,7 @@ TEST_CASE("bounds_convertible")
 #ifdef CONFIRM_COMPILATION_ERRORS
 copy(src_span_static, dst_span_static);
 #endif
+
+#if __clang__ || __GNUC__
+#pragma GCC diagnostic pop
+#endif
diff --git a/tests/multi_span_tests.cpp b/tests/multi_span_tests.cpp
index 7e3ec89..0aa0ff9 100644
--- a/tests/multi_span_tests.cpp
+++ b/tests/multi_span_tests.cpp
@@ -17,8 +17,14 @@
 #ifdef _MSC_VER
 // blanket turn off warnings from CppCoreCheck from catch
 // so people aren't annoyed by them when running the tool.
-#pragma warning(disable : 26440 26426) // from catch
+#pragma warning(disable : 26440 26426) // from catch 
+#pragma warning(disable : 4996) // multi_span is in the process of being deprecated. 
+                                // Suppressing warnings until it is completely removed
+#endif
 
+#if __clang__ || __GNUC__
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
 #endif
 
 #include <catch/catch.hpp> // for AssertionHandler, StringRef, CHECK, CHECK...
@@ -1220,6 +1226,8 @@ TEST_CASE("md_access")
             expected += 3;
         }
     }
+
+    delete[] image_ptr;
 }
 
 GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
@@ -1616,6 +1624,8 @@ TEST_CASE("span_structure_size")
     multi_span<const double, dynamic_range, 6, 4> av2 =
         as_multi_span(av1, dim(5), dim<6>(), dim<4>());
     (void) av2;
+
+    delete[] arr;
 }
 
 GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
@@ -1783,3 +1793,7 @@ TEST_CASE("iterator")
 #ifdef CONFIRM_COMPILATION_ERRORS
 copy(src_span_static, dst_span_static);
 #endif
+
+#if __clang__ || __GNUC__
+#pragma GCC diagnostic pop
+#endif
diff --git a/tests/notnull_tests.cpp b/tests/notnull_tests.cpp
index ce5a123..010dd00 100644
--- a/tests/notnull_tests.cpp
+++ b/tests/notnull_tests.cpp
@@ -234,8 +234,8 @@ void ostream_helper(T v)
     {
         std::ostringstream os;
         std::ostringstream ref;
-        os << p;
-        ref << &v;
+        os << static_cast<void*>(p);
+        ref << static_cast<void*>(&v);
         CHECK(os.str() == ref.str());
     }
     {
diff --git a/tests/strided_span_tests.cpp b/tests/strided_span_tests.cpp
index 1563d90..f201df4 100644
--- a/tests/strided_span_tests.cpp
+++ b/tests/strided_span_tests.cpp
@@ -17,8 +17,14 @@
 #ifdef _MSC_VER
 // blanket turn off warnings from CppCoreCheck from catch
 // so people aren't annoyed by them when running the tool.
-#pragma warning(disable : 26440 26426) // from catch
+#pragma warning(disable : 26440 26426) // from catch deprecated
+#pragma warning(disable : 4996) // strided_span is in the process of being deprecated. 
+                                // Suppressing warnings until it is completely removed
+#endif
 
+#if __clang__ || __GNUC__
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
 #endif
 
 #include <catch/catch.hpp> // for AssertionHandler, StringRef, CHECK, CHECK...
@@ -794,3 +800,7 @@ TEST_CASE("strided_span_conversion")
         i++;
     }
 }
+
+#if __clang__ || __GNUC__
+#pragma GCC diagnostic pop
+#endif