diff --git a/.github/workflows/ubuntu.yml b/.github/workflows/ubuntu.yml
index 1a47a885c0..d6b6540779 100644
--- a/.github/workflows/ubuntu.yml
+++ b/.github/workflows/ubuntu.yml
@@ -3,13 +3,61 @@ name: Ubuntu
 on: [push, pull_request]
 
 jobs:
-  build:
+  gcc_build:
     runs-on: ubuntu-latest
 
     steps:
     - uses: actions/checkout@v1
+    - name: install_gcc
+      run: |
+           sudo apt update
+           sudo apt install gcc-10 g++-10
+      shell: bash
     - name: cmake
       run: cmake -S . -B build -D CMAKE_BUILD_TYPE=Debug -DJSON_BuildTests=On
+      env:
+        CC:   gcc-10
+        CXX:  g++-10
+    - name: build
+      run: cmake --build build --parallel 10
+    - name: test
+      run: cd build ; ctest -j 10 --output-on-failure
+
+  clang_build:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v1
+    - name: install_gcc
+      run: |
+           sudo apt update
+           sudo apt install clang-10
+      shell: bash
+    - name: cmake
+      run: cmake -S . -B build -D CMAKE_BUILD_TYPE=Debug -DJSON_BuildTests=On
+      env:
+        CC:   clang-10
+        CXX:  clang++-10
+    - name: build
+      run: cmake --build build --parallel 10
+    - name: test
+      run: cd build ; ctest -j 10 --output-on-failure
+
+  clang_build_cxx20:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v1
+    - name: install_gcc
+      run: |
+           sudo apt update
+           sudo apt install clang-10
+      shell: bash
+    - name: cmake
+      run: cmake -S . -B build -D CMAKE_BUILD_TYPE=Debug -DJSON_BuildTests=On -DCMAKE_CXX_STANDARD=20 -DCMAKE_CXX_STANDARD_REQUIRED=ON
+      env:
+        CC:   clang-10
+        CXX:  clang++-10
     - name: build
       run: cmake --build build --parallel 10
     - name: test
diff --git a/Makefile b/Makefile
index 0b9aa8213c..d3963f503e 100644
--- a/Makefile
+++ b/Makefile
@@ -84,6 +84,7 @@ doctest:
 # -Wno-missing-prototypes: for NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE
 # -Wno-padded: padding is nothing to warn about
 # -Wno-range-loop-analysis: items tests "for(const auto i...)"
+# -Wno-extra-semi-stmt: spurious warnings for semicolons after JSON_ASSERT()
 # -Wno-switch-enum -Wno-covered-switch-default: pedantic/contradicting warnings about switches
 # -Wno-weak-vtables: exception class is defined inline, but has virtual method
 pedantic_clang:
@@ -100,6 +101,7 @@ pedantic_clang:
 		-Wno-missing-prototypes \
 		-Wno-padded \
 		-Wno-range-loop-analysis \
+		-Wno-extra-semi-stmt \
 		-Wno-switch-enum -Wno-covered-switch-default \
 		-Wno-weak-vtables" cmake -S . -B cmake-build-pedantic -GNinja -DCMAKE_BUILD_TYPE=Debug -DJSON_MultipleHeaders=ON -DJSON_BuildTests=On
 	cmake --build cmake-build-pedantic
diff --git a/include/nlohmann/detail/hash.hpp b/include/nlohmann/detail/hash.hpp
index d2d5d332d3..c32d5535c5 100644
--- a/include/nlohmann/detail/hash.hpp
+++ b/include/nlohmann/detail/hash.hpp
@@ -3,6 +3,8 @@
 #include <cstddef> // size_t, uint8_t
 #include <functional> // hash
 
+#include <nlohmann/detail/macro_scope.hpp>
+
 namespace nlohmann
 {
 namespace detail
diff --git a/include/nlohmann/detail/input/binary_reader.hpp b/include/nlohmann/detail/input/binary_reader.hpp
index 6ae5882c7e..806e360306 100644
--- a/include/nlohmann/detail/input/binary_reader.hpp
+++ b/include/nlohmann/detail/input/binary_reader.hpp
@@ -11,6 +11,7 @@
 #include <limits> // numeric_limits
 #include <string> // char_traits, string
 #include <utility> // make_pair, move
+#include <vector> // vector
 
 #include <nlohmann/detail/exceptions.hpp>
 #include <nlohmann/detail/input/input_adapters.hpp>
@@ -2340,7 +2341,7 @@ class binary_reader
                 break;
             }
             result.push_back(static_cast<typename string_t::value_type>(current));
-        };
+        }
         return success;
     }
 
diff --git a/include/nlohmann/detail/input/input_adapters.hpp b/include/nlohmann/detail/input/input_adapters.hpp
index 63921ca55c..a78a6ec96c 100644
--- a/include/nlohmann/detail/input/input_adapters.hpp
+++ b/include/nlohmann/detail/input/input_adapters.hpp
@@ -371,15 +371,37 @@ typename iterator_input_adapter_factory<IteratorType>::adapter_type input_adapte
 }
 
 // Convenience shorthand from container to iterator
-template<typename ContainerType>
-auto input_adapter(const ContainerType& container) -> decltype(input_adapter(begin(container), end(container)))
+// Enables ADL on begin(container) and end(container)
+// Encloses the using declarations in namespace for not to leak them to outside scope
+
+namespace container_input_adapter_factory_impl
 {
-    // Enable ADL
-    using std::begin;
-    using std::end;
 
+using std::begin;
+using std::end;
+
+template<typename ContainerType, typename Enable = void>
+struct container_input_adapter_factory {};
+
+template<typename ContainerType>
+struct container_input_adapter_factory< ContainerType,
+       void_t<decltype(begin(std::declval<ContainerType>()), end(std::declval<ContainerType>()))>>
+       {
+           using adapter_type = decltype(input_adapter(begin(std::declval<ContainerType>()), end(std::declval<ContainerType>())));
+
+           static adapter_type create(const ContainerType& container)
+{
     return input_adapter(begin(container), end(container));
 }
+       };
+
+}
+
+template<typename ContainerType>
+typename container_input_adapter_factory_impl::container_input_adapter_factory<ContainerType>::adapter_type input_adapter(const ContainerType& container)
+{
+    return container_input_adapter_factory_impl::container_input_adapter_factory<ContainerType>::create(container);
+}
 
 // Special cases with fast paths
 inline file_input_adapter input_adapter(std::FILE* file)
diff --git a/include/nlohmann/detail/input/lexer.hpp b/include/nlohmann/detail/input/lexer.hpp
index 0a9601352e..eae82eaa32 100644
--- a/include/nlohmann/detail/input/lexer.hpp
+++ b/include/nlohmann/detail/input/lexer.hpp
@@ -1541,17 +1541,17 @@ class lexer : public lexer_base<BasicJsonType>
             // literals
             case 't':
             {
-                std::array<char_type, 4> true_literal = {{'t', 'r', 'u', 'e'}};
+                std::array<char_type, 4> true_literal = {{char_type('t'), char_type('r'), char_type('u'), char_type('e')}};
                 return scan_literal(true_literal.data(), true_literal.size(), token_type::literal_true);
             }
             case 'f':
             {
-                std::array<char_type, 5> false_literal = {{'f', 'a', 'l', 's', 'e'}};
+                std::array<char_type, 5> false_literal = {{char_type('f'), char_type('a'), char_type('l'), char_type('s'), char_type('e')}};
                 return scan_literal(false_literal.data(), false_literal.size(), token_type::literal_false);
             }
             case 'n':
             {
-                std::array<char_type, 4> null_literal = {{'n', 'u', 'l', 'l'}};
+                std::array<char_type, 4> null_literal = {{char_type('n'), char_type('u'), char_type('l'), char_type('l')}};
                 return scan_literal(null_literal.data(), null_literal.size(), token_type::literal_null);
             }
 
diff --git a/include/nlohmann/detail/iterators/iter_impl.hpp b/include/nlohmann/detail/iterators/iter_impl.hpp
index b4faa88a5d..67134166e5 100644
--- a/include/nlohmann/detail/iterators/iter_impl.hpp
+++ b/include/nlohmann/detail/iterators/iter_impl.hpp
@@ -38,8 +38,10 @@ This class implements a both iterators (iterator and const_iterator) for the
 template<typename BasicJsonType>
 class iter_impl
 {
+    /// the iterator with BasicJsonType of different const-ness
+    using other_iter_impl = iter_impl<typename std::conditional<std::is_const<BasicJsonType>::value, typename std::remove_const<BasicJsonType>::type, const BasicJsonType>::type>;
     /// allow basic_json to access private members
-    friend iter_impl<typename std::conditional<std::is_const<BasicJsonType>::value, typename std::remove_const<BasicJsonType>::type, const BasicJsonType>::type>;
+    friend other_iter_impl;
     friend BasicJsonType;
     friend iteration_proxy<iter_impl>;
     friend iteration_proxy_value<iter_impl>;
@@ -390,10 +392,11 @@ class iter_impl
     }
 
     /*!
-    @brief  comparison: equal
+    @brief comparison: equal
     @pre The iterator is initialized; i.e. `m_object != nullptr`.
     */
-    bool operator==(const iter_impl& other) const
+    template < typename IterImpl, detail::enable_if_t < (std::is_same<IterImpl, iter_impl>::value || std::is_same<IterImpl, other_iter_impl>::value), std::nullptr_t > = nullptr >
+    bool operator==(const IterImpl& other) const
     {
         // if objects are not the same, the comparison is undefined
         if (JSON_HEDLEY_UNLIKELY(m_object != other.m_object))
@@ -417,16 +420,17 @@ class iter_impl
     }
 
     /*!
-    @brief  comparison: not equal
+    @brief comparison: not equal
     @pre The iterator is initialized; i.e. `m_object != nullptr`.
     */
-    bool operator!=(const iter_impl& other) const
+    template < typename IterImpl, detail::enable_if_t < (std::is_same<IterImpl, iter_impl>::value || std::is_same<IterImpl, other_iter_impl>::value), std::nullptr_t > = nullptr >
+    bool operator!=(const IterImpl& other) const
     {
         return !operator==(other);
     }
 
     /*!
-    @brief  comparison: smaller
+    @brief comparison: smaller
     @pre The iterator is initialized; i.e. `m_object != nullptr`.
     */
     bool operator<(const iter_impl& other) const
@@ -453,7 +457,7 @@ class iter_impl
     }
 
     /*!
-    @brief  comparison: less than or equal
+    @brief comparison: less than or equal
     @pre The iterator is initialized; i.e. `m_object != nullptr`.
     */
     bool operator<=(const iter_impl& other) const
@@ -462,7 +466,7 @@ class iter_impl
     }
 
     /*!
-    @brief  comparison: greater than
+    @brief comparison: greater than
     @pre The iterator is initialized; i.e. `m_object != nullptr`.
     */
     bool operator>(const iter_impl& other) const
@@ -471,7 +475,7 @@ class iter_impl
     }
 
     /*!
-    @brief  comparison: greater than or equal
+    @brief comparison: greater than or equal
     @pre The iterator is initialized; i.e. `m_object != nullptr`.
     */
     bool operator>=(const iter_impl& other) const
@@ -480,7 +484,7 @@ class iter_impl
     }
 
     /*!
-    @brief  add to iterator
+    @brief add to iterator
     @pre The iterator is initialized; i.e. `m_object != nullptr`.
     */
     iter_impl& operator+=(difference_type i)
@@ -509,7 +513,7 @@ class iter_impl
     }
 
     /*!
-    @brief  subtract from iterator
+    @brief subtract from iterator
     @pre The iterator is initialized; i.e. `m_object != nullptr`.
     */
     iter_impl& operator-=(difference_type i)
@@ -518,7 +522,7 @@ class iter_impl
     }
 
     /*!
-    @brief  add to iterator
+    @brief add to iterator
     @pre The iterator is initialized; i.e. `m_object != nullptr`.
     */
     iter_impl operator+(difference_type i) const
@@ -529,7 +533,7 @@ class iter_impl
     }
 
     /*!
-    @brief  addition of distance and iterator
+    @brief addition of distance and iterator
     @pre The iterator is initialized; i.e. `m_object != nullptr`.
     */
     friend iter_impl operator+(difference_type i, const iter_impl& it)
@@ -540,7 +544,7 @@ class iter_impl
     }
 
     /*!
-    @brief  subtract from iterator
+    @brief subtract from iterator
     @pre The iterator is initialized; i.e. `m_object != nullptr`.
     */
     iter_impl operator-(difference_type i) const
@@ -551,7 +555,7 @@ class iter_impl
     }
 
     /*!
-    @brief  return difference
+    @brief return difference
     @pre The iterator is initialized; i.e. `m_object != nullptr`.
     */
     difference_type operator-(const iter_impl& other) const
@@ -572,7 +576,7 @@ class iter_impl
     }
 
     /*!
-    @brief  access to successor
+    @brief access to successor
     @pre The iterator is initialized; i.e. `m_object != nullptr`.
     */
     reference operator[](difference_type n) const
@@ -603,7 +607,7 @@ class iter_impl
     }
 
     /*!
-    @brief  return the key of an object iterator
+    @brief return the key of an object iterator
     @pre The iterator is initialized; i.e. `m_object != nullptr`.
     */
     const typename object_t::key_type& key() const
@@ -619,7 +623,7 @@ class iter_impl
     }
 
     /*!
-    @brief  return the value of an iterator
+    @brief return the value of an iterator
     @pre The iterator is initialized; i.e. `m_object != nullptr`.
     */
     reference value() const
diff --git a/include/nlohmann/detail/iterators/primitive_iterator.hpp b/include/nlohmann/detail/iterators/primitive_iterator.hpp
index 16dcc9f97f..ae7471ef59 100644
--- a/include/nlohmann/detail/iterators/primitive_iterator.hpp
+++ b/include/nlohmann/detail/iterators/primitive_iterator.hpp
@@ -3,6 +3,8 @@
 #include <cstddef> // ptrdiff_t
 #include <limits>  // numeric_limits
 
+#include <nlohmann/detail/macro_scope.hpp>
+
 namespace nlohmann
 {
 namespace detail
diff --git a/include/nlohmann/detail/meta/type_traits.hpp b/include/nlohmann/detail/meta/type_traits.hpp
index 56c15a3f66..1706cbdc6a 100644
--- a/include/nlohmann/detail/meta/type_traits.hpp
+++ b/include/nlohmann/detail/meta/type_traits.hpp
@@ -3,6 +3,7 @@
 #include <limits> // numeric_limits
 #include <type_traits> // false_type, is_constructible, is_integral, is_same, true_type
 #include <utility> // declval
+#include <tuple> // tuple
 
 #include <nlohmann/detail/iterators/iterator_traits.hpp>
 #include <nlohmann/detail/macro_scope.hpp>
diff --git a/include/nlohmann/thirdparty/hedley/hedley_undef.hpp b/include/nlohmann/thirdparty/hedley/hedley_undef.hpp
index 88ee044da1..2f70f13c6d 100644
--- a/include/nlohmann/thirdparty/hedley/hedley_undef.hpp
+++ b/include/nlohmann/thirdparty/hedley/hedley_undef.hpp
@@ -1,3 +1,5 @@
+#pragma once
+
 #undef JSON_HEDLEY_ALWAYS_INLINE
 #undef JSON_HEDLEY_ARM_VERSION
 #undef JSON_HEDLEY_ARM_VERSION_CHECK
diff --git a/single_include/nlohmann/json.hpp b/single_include/nlohmann/json.hpp
index 9e988ab427..05262b84c8 100644
--- a/single_include/nlohmann/json.hpp
+++ b/single_include/nlohmann/json.hpp
@@ -2826,6 +2826,7 @@ constexpr T static_const<T>::value;
 #include <limits> // numeric_limits
 #include <type_traits> // false_type, is_constructible, is_integral, is_same, true_type
 #include <utility> // declval
+#include <tuple> // tuple
 
 // #include <nlohmann/detail/iterators/iterator_traits.hpp>
 
@@ -4710,6 +4711,9 @@ class byte_container_with_subtype : public BinaryType
 #include <cstddef> // size_t, uint8_t
 #include <functional> // hash
 
+// #include <nlohmann/detail/macro_scope.hpp>
+
+
 namespace nlohmann
 {
 namespace detail
@@ -4838,6 +4842,7 @@ std::size_t hash(const BasicJsonType& j)
 #include <limits> // numeric_limits
 #include <string> // char_traits, string
 #include <utility> // make_pair, move
+#include <vector> // vector
 
 // #include <nlohmann/detail/exceptions.hpp>
 
@@ -5217,15 +5222,37 @@ typename iterator_input_adapter_factory<IteratorType>::adapter_type input_adapte
 }
 
 // Convenience shorthand from container to iterator
-template<typename ContainerType>
-auto input_adapter(const ContainerType& container) -> decltype(input_adapter(begin(container), end(container)))
+// Enables ADL on begin(container) and end(container)
+// Encloses the using declarations in namespace for not to leak them to outside scope
+
+namespace container_input_adapter_factory_impl
 {
-    // Enable ADL
-    using std::begin;
-    using std::end;
 
+using std::begin;
+using std::end;
+
+template<typename ContainerType, typename Enable = void>
+struct container_input_adapter_factory {};
+
+template<typename ContainerType>
+struct container_input_adapter_factory< ContainerType,
+       void_t<decltype(begin(std::declval<ContainerType>()), end(std::declval<ContainerType>()))>>
+       {
+           using adapter_type = decltype(input_adapter(begin(std::declval<ContainerType>()), end(std::declval<ContainerType>())));
+
+           static adapter_type create(const ContainerType& container)
+{
     return input_adapter(begin(container), end(container));
 }
+       };
+
+}
+
+template<typename ContainerType>
+typename container_input_adapter_factory_impl::container_input_adapter_factory<ContainerType>::adapter_type input_adapter(const ContainerType& container)
+{
+    return container_input_adapter_factory_impl::container_input_adapter_factory<ContainerType>::create(container);
+}
 
 // Special cases with fast paths
 inline file_input_adapter input_adapter(std::FILE* file)
@@ -7545,17 +7572,17 @@ class lexer : public lexer_base<BasicJsonType>
             // literals
             case 't':
             {
-                std::array<char_type, 4> true_literal = {{'t', 'r', 'u', 'e'}};
+                std::array<char_type, 4> true_literal = {{char_type('t'), char_type('r'), char_type('u'), char_type('e')}};
                 return scan_literal(true_literal.data(), true_literal.size(), token_type::literal_true);
             }
             case 'f':
             {
-                std::array<char_type, 5> false_literal = {{'f', 'a', 'l', 's', 'e'}};
+                std::array<char_type, 5> false_literal = {{char_type('f'), char_type('a'), char_type('l'), char_type('s'), char_type('e')}};
                 return scan_literal(false_literal.data(), false_literal.size(), token_type::literal_false);
             }
             case 'n':
             {
-                std::array<char_type, 4> null_literal = {{'n', 'u', 'l', 'l'}};
+                std::array<char_type, 4> null_literal = {{char_type('n'), char_type('u'), char_type('l'), char_type('l')}};
                 return scan_literal(null_literal.data(), null_literal.size(), token_type::literal_null);
             }
 
@@ -10104,7 +10131,7 @@ class binary_reader
                 break;
             }
             result.push_back(static_cast<typename string_t::value_type>(current));
-        };
+        }
         return success;
     }
 
@@ -10746,6 +10773,9 @@ class parser
 #include <cstddef> // ptrdiff_t
 #include <limits>  // numeric_limits
 
+// #include <nlohmann/detail/macro_scope.hpp>
+
+
 namespace nlohmann
 {
 namespace detail
@@ -10934,8 +10964,10 @@ This class implements a both iterators (iterator and const_iterator) for the
 template<typename BasicJsonType>
 class iter_impl
 {
+    /// the iterator with BasicJsonType of different const-ness
+    using other_iter_impl = iter_impl<typename std::conditional<std::is_const<BasicJsonType>::value, typename std::remove_const<BasicJsonType>::type, const BasicJsonType>::type>;
     /// allow basic_json to access private members
-    friend iter_impl<typename std::conditional<std::is_const<BasicJsonType>::value, typename std::remove_const<BasicJsonType>::type, const BasicJsonType>::type>;
+    friend other_iter_impl;
     friend BasicJsonType;
     friend iteration_proxy<iter_impl>;
     friend iteration_proxy_value<iter_impl>;
@@ -11286,10 +11318,11 @@ class iter_impl
     }
 
     /*!
-    @brief  comparison: equal
+    @brief comparison: equal
     @pre The iterator is initialized; i.e. `m_object != nullptr`.
     */
-    bool operator==(const iter_impl& other) const
+    template < typename IterImpl, detail::enable_if_t < (std::is_same<IterImpl, iter_impl>::value || std::is_same<IterImpl, other_iter_impl>::value), std::nullptr_t > = nullptr >
+    bool operator==(const IterImpl& other) const
     {
         // if objects are not the same, the comparison is undefined
         if (JSON_HEDLEY_UNLIKELY(m_object != other.m_object))
@@ -11313,16 +11346,17 @@ class iter_impl
     }
 
     /*!
-    @brief  comparison: not equal
+    @brief comparison: not equal
     @pre The iterator is initialized; i.e. `m_object != nullptr`.
     */
-    bool operator!=(const iter_impl& other) const
+    template < typename IterImpl, detail::enable_if_t < (std::is_same<IterImpl, iter_impl>::value || std::is_same<IterImpl, other_iter_impl>::value), std::nullptr_t > = nullptr >
+    bool operator!=(const IterImpl& other) const
     {
         return !operator==(other);
     }
 
     /*!
-    @brief  comparison: smaller
+    @brief comparison: smaller
     @pre The iterator is initialized; i.e. `m_object != nullptr`.
     */
     bool operator<(const iter_impl& other) const
@@ -11349,7 +11383,7 @@ class iter_impl
     }
 
     /*!
-    @brief  comparison: less than or equal
+    @brief comparison: less than or equal
     @pre The iterator is initialized; i.e. `m_object != nullptr`.
     */
     bool operator<=(const iter_impl& other) const
@@ -11358,7 +11392,7 @@ class iter_impl
     }
 
     /*!
-    @brief  comparison: greater than
+    @brief comparison: greater than
     @pre The iterator is initialized; i.e. `m_object != nullptr`.
     */
     bool operator>(const iter_impl& other) const
@@ -11367,7 +11401,7 @@ class iter_impl
     }
 
     /*!
-    @brief  comparison: greater than or equal
+    @brief comparison: greater than or equal
     @pre The iterator is initialized; i.e. `m_object != nullptr`.
     */
     bool operator>=(const iter_impl& other) const
@@ -11376,7 +11410,7 @@ class iter_impl
     }
 
     /*!
-    @brief  add to iterator
+    @brief add to iterator
     @pre The iterator is initialized; i.e. `m_object != nullptr`.
     */
     iter_impl& operator+=(difference_type i)
@@ -11405,7 +11439,7 @@ class iter_impl
     }
 
     /*!
-    @brief  subtract from iterator
+    @brief subtract from iterator
     @pre The iterator is initialized; i.e. `m_object != nullptr`.
     */
     iter_impl& operator-=(difference_type i)
@@ -11414,7 +11448,7 @@ class iter_impl
     }
 
     /*!
-    @brief  add to iterator
+    @brief add to iterator
     @pre The iterator is initialized; i.e. `m_object != nullptr`.
     */
     iter_impl operator+(difference_type i) const
@@ -11425,7 +11459,7 @@ class iter_impl
     }
 
     /*!
-    @brief  addition of distance and iterator
+    @brief addition of distance and iterator
     @pre The iterator is initialized; i.e. `m_object != nullptr`.
     */
     friend iter_impl operator+(difference_type i, const iter_impl& it)
@@ -11436,7 +11470,7 @@ class iter_impl
     }
 
     /*!
-    @brief  subtract from iterator
+    @brief subtract from iterator
     @pre The iterator is initialized; i.e. `m_object != nullptr`.
     */
     iter_impl operator-(difference_type i) const
@@ -11447,7 +11481,7 @@ class iter_impl
     }
 
     /*!
-    @brief  return difference
+    @brief return difference
     @pre The iterator is initialized; i.e. `m_object != nullptr`.
     */
     difference_type operator-(const iter_impl& other) const
@@ -11468,7 +11502,7 @@ class iter_impl
     }
 
     /*!
-    @brief  access to successor
+    @brief access to successor
     @pre The iterator is initialized; i.e. `m_object != nullptr`.
     */
     reference operator[](difference_type n) const
@@ -11499,7 +11533,7 @@ class iter_impl
     }
 
     /*!
-    @brief  return the key of an object iterator
+    @brief return the key of an object iterator
     @pre The iterator is initialized; i.e. `m_object != nullptr`.
     */
     const typename object_t::key_type& key() const
@@ -11515,7 +11549,7 @@ class iter_impl
     }
 
     /*!
-    @brief  return the value of an iterator
+    @brief return the value of an iterator
     @pre The iterator is initialized; i.e. `m_object != nullptr`.
     */
     reference value() const
@@ -25449,6 +25483,8 @@ inline nlohmann::json::json_pointer operator "" _json_pointer(const char* s, std
 #undef JSON_EXPLICIT
 
 // #include <nlohmann/thirdparty/hedley/hedley_undef.hpp>
+
+
 #undef JSON_HEDLEY_ALWAYS_INLINE
 #undef JSON_HEDLEY_ARM_VERSION
 #undef JSON_HEDLEY_ARM_VERSION_CHECK
diff --git a/test/src/unit-class_lexer.cpp b/test/src/unit-class_lexer.cpp
index 1a4f8ed754..07d243a818 100644
--- a/test/src/unit-class_lexer.cpp
+++ b/test/src/unit-class_lexer.cpp
@@ -135,7 +135,7 @@ TEST_CASE("lexer class")
             // store scan() result
             const auto res = scan_string(s.c_str());
 
-            CAPTURE(s);
+            CAPTURE(s)
 
             switch (c)
             {
diff --git a/test/src/unit-class_parser.cpp b/test/src/unit-class_parser.cpp
index d0335c9484..2df07d6d44 100644
--- a/test/src/unit-class_parser.cpp
+++ b/test/src/unit-class_parser.cpp
@@ -509,7 +509,7 @@ TEST_CASE("parser class")
                 CHECK(parser_helper("\"€\"").get<json::string_t>() == "€");
                 CHECK(parser_helper("\"🎈\"").get<json::string_t>() == "🎈");
 
-                CHECK(parser_helper("\"\\ud80c\\udc60\"").get<json::string_t>() == u8"\U00013060");
+                CHECK(parser_helper("\"\\ud80c\\udc60\"").get<json::string_t>() == "\xf0\x93\x81\xa0");
                 CHECK(parser_helper("\"\\ud83c\\udf1e\"").get<json::string_t>() == "🌞");
             }
         }
diff --git a/test/src/unit-conversions.cpp b/test/src/unit-conversions.cpp
index 0d5baa409d..6de003d806 100644
--- a/test/src/unit-conversions.cpp
+++ b/test/src/unit-conversions.cpp
@@ -1761,3 +1761,11 @@ TEST_CASE("std::optional")
     }
 }
 #endif
+
+#ifdef JSON_HAS_CPP_17
+    #undef JSON_HAS_CPP_17
+#endif
+
+#ifdef JSON_HAS_CPP_14
+    #undef JSON_HAS_CPP_14
+#endif
diff --git a/test/src/unit-items.cpp b/test/src/unit-items.cpp
index 10621ce7e9..4caf76f237 100644
--- a/test/src/unit-items.cpp
+++ b/test/src/unit-items.cpp
@@ -1448,3 +1448,11 @@ TEST_CASE("items()")
         }
     }
 }
+
+#ifdef JSON_HAS_CPP_17
+    #undef JSON_HAS_CPP_17
+#endif
+
+#ifdef JSON_HAS_CPP_14
+    #undef JSON_HAS_CPP_14
+#endif
diff --git a/test/src/unit-regression1.cpp b/test/src/unit-regression1.cpp
index 9dcc75b092..df660ddb4b 100644
--- a/test/src/unit-regression1.cpp
+++ b/test/src/unit-regression1.cpp
@@ -400,7 +400,7 @@ TEST_CASE("regression tests 1")
 
     SECTION("issue #146 - character following a surrogate pair is skipped")
     {
-        CHECK(json::parse("\"\\ud80c\\udc60abc\"").get<json::string_t>() == u8"\U00013060abc");
+        CHECK(json::parse("\"\\ud80c\\udc60abc\"").get<json::string_t>() == "\xf0\x93\x81\xa0\x61\x62\x63");
     }
 
     SECTION("issue #171 - Cannot index by key of type static constexpr const char*")
diff --git a/test/src/unit-regression2.cpp b/test/src/unit-regression2.cpp
index ca50cdd41d..1e8c4922a7 100644
--- a/test/src/unit-regression2.cpp
+++ b/test/src/unit-regression2.cpp
@@ -51,6 +51,10 @@ using nlohmann::json;
     #include <variant>
 #endif
 
+#ifdef JSON_HAS_CPP_20
+    #include <span>
+#endif
+
 /////////////////////////////////////////////////////////////////////
 // for #1021
 /////////////////////////////////////////////////////////////////////
@@ -484,4 +488,14 @@ TEST_CASE("regression tests 2")
         json j = json::parse(ss, nullptr, true, true);
         CHECK(j.dump() == "{}");
     }
+
+#ifdef JSON_HAS_CPP_20
+    SECTION("issue #2546 - parsing containers of std::byte")
+    {
+        const char DATA[] = R"("Hello, world!")";
+        const auto s = std::as_bytes(std::span(DATA));
+        json j = json::parse(s);
+        CHECK(j.dump() == "\"Hello, world!\"");
+    }
+#endif
 }
diff --git a/test/src/unit-udt.cpp b/test/src/unit-udt.cpp
index 7f74ac5f8b..b237655056 100644
--- a/test/src/unit-udt.cpp
+++ b/test/src/unit-udt.cpp
@@ -112,13 +112,13 @@ static void to_json(BasicJsonType& j, country c)
     switch (c)
     {
         case country::china:
-            j = u8"中华人民共和国";
+            j = "中华人民共和国";
             return;
         case country::france:
             j = "France";
             return;
         case country::russia:
-            j = u8"Российская Федерация";
+            j = "Российская Федерация";
             return;
         default:
             break;
@@ -201,9 +201,9 @@ static void from_json(const BasicJsonType& j, country& c)
     const auto str = j.template get<std::string>();
     static const std::map<std::string, country> m =
     {
-        {u8"中华人民共和国", country::china},
+        {"中华人民共和国", country::china},
         {"France", country::france},
-        {u8"Российская Федерация", country::russia}
+        {"Российская Федерация", country::russia}
     };
 
     const auto it = m.find(str);
@@ -248,7 +248,7 @@ TEST_CASE("basic usage" * doctest::test_suite("udt"))
     const udt::name n{"theo"};
     const udt::country c{udt::country::france};
     const udt::person sfinae_addict{a, n, c};
-    const udt::person senior_programmer{{42}, {u8"王芳"}, udt::country::china};
+    const udt::person senior_programmer{{42}, {"王芳"}, udt::country::china};
     const udt::address addr{"Paris"};
     const udt::contact cpp_programmer{sfinae_addict, addr};
     const udt::contact_book book{{"C++"}, {cpp_programmer, {senior_programmer, addr}}};
@@ -265,14 +265,14 @@ TEST_CASE("basic usage" * doctest::test_suite("udt"))
 
         CHECK(
             json(book) ==
-            u8R"({"name":"C++", "contacts" : [{"person" : {"age":23, "name":"theo", "country":"France"}, "address":"Paris"}, {"person" : {"age":42, "country":"中华人民共和国", "name":"王芳"}, "address":"Paris"}]})"_json);
+            R"({"name":"C++", "contacts" : [{"person" : {"age":23, "name":"theo", "country":"France"}, "address":"Paris"}, {"person" : {"age":42, "country":"中华人民共和国", "name":"王芳"}, "address":"Paris"}]})"_json);
 
     }
 
     SECTION("conversion from json via free-functions")
     {
         const auto big_json =
-            u8R"({"name":"C++", "contacts" : [{"person" : {"age":23, "name":"theo", "country":"France"}, "address":"Paris"}, {"person" : {"age":42, "country":"中华人民共和国", "name":"王芳"}, "address":"Paris"}]})"_json;
+            R"({"name":"C++", "contacts" : [{"person" : {"age":23, "name":"theo", "country":"France"}, "address":"Paris"}, {"person" : {"age":42, "country":"中华人民共和国", "name":"王芳"}, "address":"Paris"}]})"_json;
         SECTION("via explicit calls to get")
         {
             const auto parsed_book = big_json.get<udt::contact_book>();
diff --git a/test/src/unit-udt_macro.cpp b/test/src/unit-udt_macro.cpp
index b56a5d15e2..a13ac006b3 100644
--- a/test/src/unit-udt_macro.cpp
+++ b/test/src/unit-udt_macro.cpp
@@ -106,7 +106,7 @@ NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(person_without_private_data_2, age, name, met
 class person_with_private_alphabet
 {
   public:
-    bool operator==(const person_with_private_alphabet& other)
+    bool operator==(const person_with_private_alphabet& other) const
     {
         return  a == other.a &&
                 b == other.b &&
@@ -169,7 +169,7 @@ class person_with_private_alphabet
 class person_with_public_alphabet
 {
   public:
-    bool operator==(const person_with_public_alphabet& other)
+    bool operator==(const person_with_public_alphabet& other) const
     {
         return  a == other.a &&
                 b == other.b &&
diff --git a/test/src/unit-user_defined_input.cpp b/test/src/unit-user_defined_input.cpp
index 5a1138b004..4b84e8e71c 100644
--- a/test/src/unit-user_defined_input.cpp
+++ b/test/src/unit-user_defined_input.cpp
@@ -63,7 +63,7 @@ const char* end(const MyContainer& c)
     return c.data + strlen(c.data);
 }
 
-TEST_CASE("Custom container")
+TEST_CASE("Custom container non-member begin/end")
 {
 
     MyContainer data{"[1,2,3,4]"};
@@ -75,6 +75,31 @@ TEST_CASE("Custom container")
 
 }
 
+TEST_CASE("Custom container member begin/end")
+{
+    struct MyContainer2
+    {
+        const char* data;
+
+        const char* begin() const
+        {
+            return data;
+        }
+
+        const char* end() const
+        {
+            return data + strlen(data);
+        }
+    };
+
+    MyContainer2 data{"[1,2,3,4]"};
+    json as_json = json::parse(data);
+    CHECK(as_json.at(0) == 1);
+    CHECK(as_json.at(1) == 2);
+    CHECK(as_json.at(2) == 3);
+    CHECK(as_json.at(3) == 4);
+}
+
 TEST_CASE("Custom iterator")
 {
     const char* raw_data = "[1,2,3,4]";