diff --git a/.cmake-format.yaml b/.cmake-format.yaml
index c80494f1..b1465f47 100644
--- a/.cmake-format.yaml
+++ b/.cmake-format.yaml
@@ -10,9 +10,15 @@ parse:
     enable_iwyu:
       pargs:
         flags:
+          - QUIET
+          - REQUIRED
           - NO_FORWARD_DECLARATIONS
-          - QUOTED_INCLUDES_FIRST
+          - PCH_IN_CODE
+          - TRANSITIVE_INCLUDES_ONLY
           - NO_COMMENTS
+          - NO_FORWARD_DECLARATIONS
+          - CXX17_NAMESPACES
+          - QUOTED_INCLUDES_FIRST
       kwargs:
         MAPPING_FILE: 1
         MAX_LINE_LENGTH: 1
diff --git a/cmake/include-what-you-use.cmake b/cmake/include-what-you-use.cmake
index 2f3e69ed..f42bebc4 100644
--- a/cmake/include-what-you-use.cmake
+++ b/cmake/include-what-you-use.cmake
@@ -45,6 +45,7 @@ macro(_process_iwyu_arguments offset log_postfix)
     set(_options
         QUIET
         REQUIRED
+        ERROR
         NO_DEFAULT_MAPPINGS
         PCH_IN_CODE
         TRANSITIVE_INCLUDES_ONLY
@@ -112,6 +113,7 @@ macro(_process_iwyu_arguments offset log_postfix)
         _iwyu_args_append("--max_line_length=${_enable_iwyu_MAX_LINE_LENGTH}")
     endif()
 
+    _iwyu_args_append_if_present(ERROR "--error")
     _iwyu_args_append_if_present(NO_DEFAULT_MAPPINGS "--no_default_mappings")
     _iwyu_args_append_if_present(PCH_IN_CODE "--pch_in_code")
     _iwyu_args_append_if_present(TRANSITIVE_INCLUDES_ONLY "--transitive_includes_only")
diff --git a/example/avg_speed.cpp b/example/avg_speed.cpp
index a31f6a1b..f7f5e611 100644
--- a/example/avg_speed.cpp
+++ b/example/avg_speed.cpp
@@ -33,8 +33,8 @@ import mp_units;
 #include <mp-units/ostream.h>
 #include <mp-units/systems/cgs/cgs.h>
 #include <mp-units/systems/international/international.h>
-#include <mp-units/systems/isq/space_and_time.h>
-#include <mp-units/systems/si/unit_symbols.h>
+#include <mp-units/systems/isq/isq.h>
+#include <mp-units/systems/si/si.h>
 #endif
 
 namespace {
diff --git a/example/capacitor_time_curve.cpp b/example/capacitor_time_curve.cpp
index 02bbc271..fc9f867b 100644
--- a/example/capacitor_time_curve.cpp
+++ b/example/capacitor_time_curve.cpp
@@ -24,7 +24,7 @@
 #ifdef MP_UNITS_MODULES
 import mp_units;
 #else
-#include <mp-units/math.h>  // IWYU pragma: keep
+#include <mp-units/math.h>
 #include <mp-units/ostream.h>
 #include <mp-units/systems/isq/electromagnetism.h>
 #include <mp-units/systems/si/si.h>
diff --git a/example/conversion_factor.cpp b/example/conversion_factor.cpp
index 308fb2a0..a4d577a8 100644
--- a/example/conversion_factor.cpp
+++ b/example/conversion_factor.cpp
@@ -16,15 +16,14 @@
 */
 
 #include <mp-units/compat_macros.h>
+#include <concepts>
 #include <iostream>
-#include <type_traits>
+#include <string>
 #ifdef MP_UNITS_MODULES
 import mp_units;
 #else
 #include <mp-units/format.h>
-#include <mp-units/systems/isq/space_and_time.h>
-#include <mp-units/systems/si/unit_symbols.h>
-#include <mp-units/systems/si/units.h>
+#include <mp-units/systems/si/si.h>
 #endif
 
 /*
diff --git a/example/currency.cpp b/example/currency.cpp
index cc935c5e..c81786fb 100644
--- a/example/currency.cpp
+++ b/example/currency.cpp
@@ -21,14 +21,16 @@
 // SOFTWARE.
 
 #include <mp-units/compat_macros.h>
+#include <concepts>
 #include <iostream>
 #include <map>
+#include <string_view>
+#include <utility>
 #ifdef MP_UNITS_MODULES
 import mp_units.core;
 #else
+#include <mp-units/framework.h>
 #include <mp-units/ostream.h>
-#include <mp-units/quantity.h>
-#include <mp-units/quantity_point.h>
 #endif
 
 using namespace mp_units;
diff --git a/example/glide_computer_lib/include/glide_computer_lib.h b/example/glide_computer_lib/include/glide_computer_lib.h
index b198dabf..5a1faaf7 100644
--- a/example/glide_computer_lib/include/glide_computer_lib.h
+++ b/example/glide_computer_lib/include/glide_computer_lib.h
@@ -36,8 +36,8 @@
 #ifdef MP_UNITS_MODULES
 import mp_units;
 #else
+#include <mp-units/framework/quantity_point.h>
 #include <mp-units/math.h>  // IWYU pragma: keep
-#include <mp-units/quantity_point.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/si/chrono.h>
 #endif
diff --git a/example/include/geographic.h b/example/include/geographic.h
index e2b92124..06349d16 100644
--- a/example/include/geographic.h
+++ b/example/include/geographic.h
@@ -31,10 +31,8 @@
 #ifdef MP_UNITS_MODULES
 import mp_units;
 #else
-#include <mp-units/compare.h>
 #include <mp-units/format.h>
-#include <mp-units/quantity.h>
-#include <mp-units/quantity_point.h>
+#include <mp-units/framework.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/si/si.h>
 #endif
diff --git a/example/include/ranged_representation.h b/example/include/ranged_representation.h
index 0f760c00..9fc493cd 100644
--- a/example/include/ranged_representation.h
+++ b/example/include/ranged_representation.h
@@ -23,7 +23,7 @@
 #pragma once
 
 #include "validated_type.h"
-#include <mp-units/bits/external/hacks.h>
+#include <mp-units/bits/hacks.h>
 #include <mp-units/compat_macros.h>
 #include <algorithm>
 #include <concepts>
@@ -32,7 +32,7 @@
 import mp_units.core;
 #else
 #include <mp-units/bits/fmt.h>
-#include <mp-units/customization_points.h>
+#include <mp-units/framework/customization_points.h>
 #endif
 
 template<std::movable T, MP_UNITS_CONSTRAINED_NTTP_WORKAROUND(std::convertible_to<T>) auto Min,
diff --git a/example/include/validated_type.h b/example/include/validated_type.h
index 8be7c1a6..738c42e6 100644
--- a/example/include/validated_type.h
+++ b/example/include/validated_type.h
@@ -23,16 +23,17 @@
 #pragma once
 
 #include <gsl/gsl-lite.hpp>
-#include <mp-units/bits/external/hacks.h>
+#include <mp-units/bits/hacks.h>
 #include <mp-units/compat_macros.h>
+#include <compare>  // IWYU pragma: export
 #include <ostream>
 #include <utility>
 #ifdef MP_UNITS_MODULES
 import mp_units.core;
 #else
-#include <mp-units/bits/external/hacks.h>
 #include <mp-units/bits/fmt.h>
-#include <mp-units/customization_points.h>
+#include <mp-units/bits/hacks.h>
+#include <mp-units/framework/customization_points.h>
 #endif
 
 inline constexpr struct validated_tag {
diff --git a/example/measurement.cpp b/example/measurement.cpp
index 8a6a5948..52e991e7 100644
--- a/example/measurement.cpp
+++ b/example/measurement.cpp
@@ -20,17 +20,21 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
+#include <mp-units/bits/hacks.h>
 #include <mp-units/compat_macros.h>
 #include <cmath>
+#include <compare>  // IWYU pragma: export
+#include <cstdlib>
 #include <exception>
 #include <iostream>
+#include <utility>
 #ifdef MP_UNITS_MODULES
 import mp_units;
 #else
+#include <mp-units/framework.h>
 #include <mp-units/ostream.h>
 #include <mp-units/systems/isq/space_and_time.h>
-#include <mp-units/systems/si/unit_symbols.h>
-#include <mp-units/systems/si/units.h>
+#include <mp-units/systems/si/si.h>
 #endif
 
 namespace {
diff --git a/example/storage_tank.cpp b/example/storage_tank.cpp
index 74de7482..76f2af8e 100644
--- a/example/storage_tank.cpp
+++ b/example/storage_tank.cpp
@@ -25,7 +25,7 @@
 #include <chrono>
 #include <iostream>
 #include <numbers>
-#include <utility>
+#include <string>
 #ifdef MP_UNITS_MODULES
 import mp_units;
 #else
diff --git a/example/strong_angular_quantities.cpp b/example/strong_angular_quantities.cpp
index 298a097e..585e5b01 100644
--- a/example/strong_angular_quantities.cpp
+++ b/example/strong_angular_quantities.cpp
@@ -24,10 +24,9 @@
 #ifdef MP_UNITS_MODULES
 import mp_units;
 #else
-#include <mp-units/math.h>
 #include <mp-units/ostream.h>
 #include <mp-units/systems/isq_angle/isq_angle.h>
-#include <mp-units/systems/si/unit_symbols.h>
+#include <mp-units/systems/si/si.h>
 #endif
 
 template<class T>
diff --git a/example/total_energy.cpp b/example/total_energy.cpp
index aea49059..64f93aa3 100644
--- a/example/total_energy.cpp
+++ b/example/total_energy.cpp
@@ -28,9 +28,9 @@ import mp_units;
 #include <mp-units/math.h>
 #include <mp-units/ostream.h>
 #include <mp-units/systems/isq/mechanics.h>
+#include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/natural/natural.h>
-#include <mp-units/systems/si/constants.h>
-#include <mp-units/systems/si/unit_symbols.h>
+#include <mp-units/systems/si/si.h>
 #endif
 
 template<class T>
diff --git a/example/unmanned_aerial_vehicle.cpp b/example/unmanned_aerial_vehicle.cpp
index e520fd4d..19b68922 100644
--- a/example/unmanned_aerial_vehicle.cpp
+++ b/example/unmanned_aerial_vehicle.cpp
@@ -27,8 +27,8 @@
 #ifdef MP_UNITS_MODULES
 import mp_units;
 #else
+#include <mp-units/framework/quantity_point.h>
 #include <mp-units/ostream.h>
-#include <mp-units/quantity_point.h>
 #include <mp-units/systems/international/international.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/si/unit_symbols.h>
diff --git a/src/core/CMakeLists.txt b/src/core/CMakeLists.txt
index 329ec1ec..e893d85f 100644
--- a/src/core/CMakeLists.txt
+++ b/src/core/CMakeLists.txt
@@ -40,50 +40,51 @@ endif()
 add_mp_units_module(
     core mp-units-core
     DEPENDENCIES gsl::gsl-lite
-    HEADERS include/mp-units/bits/external/algorithm.h
-            include/mp-units/bits/external/fixed_string.h
-            include/mp-units/bits/external/hacks.h
-            include/mp-units/bits/external/math_concepts.h
-            include/mp-units/bits/external/prime.h
-            include/mp-units/bits/external/type_list.h
-            include/mp-units/bits/external/type_name.h
-            include/mp-units/bits/external/type_traits.h
-            include/mp-units/bits/core_gmf.h
-            include/mp-units/bits/dimension_concepts.h
-            include/mp-units/bits/expression_template.h
+    HEADERS include/mp-units/bits/core_gmf.h
             include/mp-units/bits/fmt.h
             include/mp-units/bits/get_associated_quantity.h
             include/mp-units/bits/get_common_base.h
-            include/mp-units/bits/magnitude.h
+            include/mp-units/bits/hacks.h
+            include/mp-units/bits/math_concepts.h
             include/mp-units/bits/module_macros.h
-            include/mp-units/bits/quantity_cast.h
-            include/mp-units/bits/quantity_concepts.h
-            include/mp-units/bits/quantity_point_concepts.h
-            include/mp-units/bits/quantity_spec_concepts.h
             include/mp-units/bits/ratio.h
-            include/mp-units/bits/reference_concepts.h
-            include/mp-units/bits/representation_concepts.h
             include/mp-units/bits/sudo_cast.h
-            include/mp-units/bits/symbol_text.h
             include/mp-units/bits/text_tools.h
-            include/mp-units/bits/unit_concepts.h
-            include/mp-units/bits/value_cast.h
-            include/mp-units/compare.h
+            include/mp-units/bits/type_list.h
+            include/mp-units/ext/algorithm.h
+            include/mp-units/ext/fixed_string.h
+            include/mp-units/ext/prime.h
+            include/mp-units/ext/type_name.h
+            include/mp-units/ext/type_traits.h
+            include/mp-units/framework/compare.h
+            include/mp-units/framework/customization_points.h
+            include/mp-units/framework/dimension.h
+            include/mp-units/framework/dimension_concepts.h
+            include/mp-units/framework/expression_template.h
+            include/mp-units/framework/magnitude.h
+            include/mp-units/framework/quantity.h
+            include/mp-units/framework/quantity_cast.h
+            include/mp-units/framework/quantity_concepts.h
+            include/mp-units/framework/quantity_point.h
+            include/mp-units/framework/quantity_point_concepts.h
+            include/mp-units/framework/quantity_spec.h
+            include/mp-units/framework/quantity_spec_concepts.h
+            include/mp-units/framework/reference.h
+            include/mp-units/framework/reference_concepts.h
+            include/mp-units/framework/representation_concepts.h
+            include/mp-units/framework/symbol_text.h
+            include/mp-units/framework/system_reference.h
+            include/mp-units/framework/unit.h
+            include/mp-units/framework/unit_concepts.h
+            include/mp-units/framework/value_cast.h
             include/mp-units/compat_macros.h
             include/mp-units/concepts.h
             include/mp-units/core.h
-            include/mp-units/customization_points.h
-            include/mp-units/dimension.h
             include/mp-units/format.h
+            include/mp-units/framework.h
             include/mp-units/math.h
             include/mp-units/ostream.h
-            include/mp-units/quantity.h
-            include/mp-units/quantity_point.h
-            include/mp-units/quantity_spec.h
             include/mp-units/random.h
-            include/mp-units/reference.h
-            include/mp-units/system_reference.h
-            include/mp-units/unit.h
     MODULE_INTERFACE_UNIT mp-units-core.cpp
 )
 
diff --git a/src/core/include/mp-units/bits/core_gmf.h b/src/core/include/mp-units/bits/core_gmf.h
index 0c200a6c..261baca5 100644
--- a/src/core/include/mp-units/bits/core_gmf.h
+++ b/src/core/include/mp-units/bits/core_gmf.h
@@ -23,7 +23,7 @@
 #pragma once
 
 #include <gsl/gsl-lite.hpp>
-#include <mp-units/bits/external/hacks.h>
+#include <mp-units/bits/hacks.h>
 #include <mp-units/compat_macros.h>
 #include <array>
 #include <cmath>
diff --git a/src/core/include/mp-units/bits/get_associated_quantity.h b/src/core/include/mp-units/bits/get_associated_quantity.h
index abaee2a3..2a474303 100644
--- a/src/core/include/mp-units/bits/get_associated_quantity.h
+++ b/src/core/include/mp-units/bits/get_associated_quantity.h
@@ -22,9 +22,9 @@
 
 #pragma once
 
-#include <mp-units/bits/expression_template.h>
-#include <mp-units/bits/unit_concepts.h>
-#include <mp-units/quantity_spec.h>
+#include <mp-units/framework/expression_template.h>
+#include <mp-units/framework/quantity_spec.h>
+#include <mp-units/framework/unit_concepts.h>
 
 namespace mp_units::detail {
 
diff --git a/src/core/include/mp-units/bits/get_common_base.h b/src/core/include/mp-units/bits/get_common_base.h
index 97ad5fbd..e703a41f 100644
--- a/src/core/include/mp-units/bits/get_common_base.h
+++ b/src/core/include/mp-units/bits/get_common_base.h
@@ -22,7 +22,7 @@
 
 #pragma once
 
-#include <mp-units/bits/quantity_spec_concepts.h>
+#include <mp-units/framework/quantity_spec_concepts.h>
 
 namespace mp_units::detail {
 
diff --git a/src/core/include/mp-units/bits/external/hacks.h b/src/core/include/mp-units/bits/hacks.h
similarity index 100%
rename from src/core/include/mp-units/bits/external/hacks.h
rename to src/core/include/mp-units/bits/hacks.h
diff --git a/src/core/include/mp-units/bits/external/math_concepts.h b/src/core/include/mp-units/bits/math_concepts.h
similarity index 100%
rename from src/core/include/mp-units/bits/external/math_concepts.h
rename to src/core/include/mp-units/bits/math_concepts.h
diff --git a/src/core/include/mp-units/bits/ratio.h b/src/core/include/mp-units/bits/ratio.h
index 8ca88b58..872a82ce 100644
--- a/src/core/include/mp-units/bits/ratio.h
+++ b/src/core/include/mp-units/bits/ratio.h
@@ -22,12 +22,12 @@
 
 #pragma once
 
-#include <mp-units/bits/external/hacks.h>
+#include <mp-units/bits/hacks.h>
 #include <mp-units/bits/module_macros.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <gsl/gsl-lite.hpp>
-#include <compare>
+#include <compare>  // IWYU pragma: export
 #include <cstdint>
 #include <numeric>
 #endif
diff --git a/src/core/include/mp-units/bits/sudo_cast.h b/src/core/include/mp-units/bits/sudo_cast.h
index 65efb882..65e4ea2a 100644
--- a/src/core/include/mp-units/bits/sudo_cast.h
+++ b/src/core/include/mp-units/bits/sudo_cast.h
@@ -22,11 +22,11 @@
 
 #pragma once
 
-#include <mp-units/bits/external/type_traits.h>
-#include <mp-units/bits/magnitude.h>
-#include <mp-units/bits/quantity_concepts.h>
-#include <mp-units/bits/reference_concepts.h>
-#include <mp-units/unit.h>
+#include <mp-units/ext/type_traits.h>
+#include <mp-units/framework/magnitude.h>
+#include <mp-units/framework/quantity_concepts.h>
+#include <mp-units/framework/reference_concepts.h>
+#include <mp-units/framework/unit.h>
 
 namespace mp_units::detail {
 
diff --git a/src/core/include/mp-units/bits/text_tools.h b/src/core/include/mp-units/bits/text_tools.h
index 35ab0c4c..a2691b74 100644
--- a/src/core/include/mp-units/bits/text_tools.h
+++ b/src/core/include/mp-units/bits/text_tools.h
@@ -22,18 +22,16 @@
 
 #pragma once
 
-#include <mp-units/bits/external/fixed_string.h>
-#include <mp-units/bits/external/type_traits.h>
 #include <mp-units/bits/ratio.h>
-#include <mp-units/bits/symbol_text.h>
+#include <mp-units/ext/fixed_string.h>
+#include <mp-units/ext/type_traits.h>
+#include <mp-units/framework/symbol_text.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <cstdint>
 #endif
 
-namespace mp_units {
-
-namespace detail {
+namespace mp_units::detail {
 
 template<std::intmax_t Value>
   requires(0 <= Value) && (Value < 10)
@@ -92,16 +90,6 @@ template<std::intmax_t Value>
     return regular<Value / 10>() + regular<Value % 10>();
 }
 
-}  // namespace detail
-
-MP_UNITS_EXPORT enum class text_encoding : std::int8_t {
-  unicode,  // µs; m³;  L²MT⁻³
-  ascii,    // us; m^3; L^2MT^-3
-  default_encoding = unicode
-};
-
-namespace detail {
-
 template<typename CharT, std::size_t N, std::size_t M, std::output_iterator<CharT> Out>
 constexpr Out copy(const symbol_text<N, M>& txt, text_encoding encoding, Out out)
 {
@@ -159,6 +147,4 @@ constexpr Out copy_symbol_exponent(text_encoding encoding, bool negative_power,
   }
 }
 
-}  // namespace detail
-
-}  // namespace mp_units
+}  // namespace mp_units::detail
diff --git a/src/core/include/mp-units/bits/external/type_list.h b/src/core/include/mp-units/bits/type_list.h
similarity index 99%
rename from src/core/include/mp-units/bits/external/type_list.h
rename to src/core/include/mp-units/bits/type_list.h
index 90fec0b6..0f27c413 100644
--- a/src/core/include/mp-units/bits/external/type_list.h
+++ b/src/core/include/mp-units/bits/type_list.h
@@ -22,7 +22,7 @@
 
 #pragma once
 
-#include <mp-units/bits/external/hacks.h>  // IWYU pragma: keep
+#include <mp-units/bits/hacks.h>  // IWYU pragma: keep
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <cstddef>
diff --git a/src/core/include/mp-units/compat_macros.h b/src/core/include/mp-units/compat_macros.h
index 0c3c9876..b9897338 100644
--- a/src/core/include/mp-units/compat_macros.h
+++ b/src/core/include/mp-units/compat_macros.h
@@ -20,9 +20,11 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
+// IWYU pragma: always_keep
+
 #pragma once
 
-#include <mp-units/bits/external/hacks.h>
+#include <mp-units/bits/hacks.h>
 
 #ifdef MP_UNITS_API_NO_CRTP
 
diff --git a/src/core/include/mp-units/concepts.h b/src/core/include/mp-units/concepts.h
index 1cd93c78..ebd5dee9 100644
--- a/src/core/include/mp-units/concepts.h
+++ b/src/core/include/mp-units/concepts.h
@@ -22,10 +22,12 @@
 
 #pragma once
 
-#include <mp-units/bits/dimension_concepts.h>
-#include <mp-units/bits/quantity_concepts.h>
-#include <mp-units/bits/quantity_point_concepts.h>
-#include <mp-units/bits/quantity_spec_concepts.h>
-#include <mp-units/bits/reference_concepts.h>
-#include <mp-units/bits/representation_concepts.h>
-#include <mp-units/bits/unit_concepts.h>
+// IWYU pragma: begin_exports
+#include <mp-units/framework/dimension_concepts.h>
+#include <mp-units/framework/quantity_concepts.h>
+#include <mp-units/framework/quantity_point_concepts.h>
+#include <mp-units/framework/quantity_spec_concepts.h>
+#include <mp-units/framework/reference_concepts.h>
+#include <mp-units/framework/representation_concepts.h>
+#include <mp-units/framework/unit_concepts.h>
+// IWYU pragma: end_exports
diff --git a/src/core/include/mp-units/core.h b/src/core/include/mp-units/core.h
index d2d49551..02be2641 100644
--- a/src/core/include/mp-units/core.h
+++ b/src/core/include/mp-units/core.h
@@ -22,18 +22,12 @@
 
 #pragma once
 
-#include <mp-units/compare.h>
+// IWYU pragma: begin_exports
 #include <mp-units/compat_macros.h>
 #include <mp-units/concepts.h>
-#include <mp-units/customization_points.h>
-#include <mp-units/dimension.h>
 #include <mp-units/format.h>
+#include <mp-units/framework.h>
 #include <mp-units/math.h>
 #include <mp-units/ostream.h>
-#include <mp-units/quantity.h>
-#include <mp-units/quantity_point.h>
-#include <mp-units/quantity_spec.h>
 #include <mp-units/random.h>
-#include <mp-units/reference.h>
-#include <mp-units/system_reference.h>
-#include <mp-units/unit.h>
+// IWYU pragma: end_exports
diff --git a/src/core/include/mp-units/bits/external/algorithm.h b/src/core/include/mp-units/ext/algorithm.h
similarity index 99%
rename from src/core/include/mp-units/bits/external/algorithm.h
rename to src/core/include/mp-units/ext/algorithm.h
index 4464efef..4161cbb9 100644
--- a/src/core/include/mp-units/bits/external/algorithm.h
+++ b/src/core/include/mp-units/ext/algorithm.h
@@ -22,7 +22,7 @@
 
 #pragma once
 
-#include <mp-units/bits/external/hacks.h>  // IWYU pragma: keep
+#include <mp-units/bits/hacks.h>  // IWYU pragma: keep
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <compare>
diff --git a/src/core/include/mp-units/bits/external/fixed_string.h b/src/core/include/mp-units/ext/fixed_string.h
similarity index 98%
rename from src/core/include/mp-units/bits/external/fixed_string.h
rename to src/core/include/mp-units/ext/fixed_string.h
index 402140c1..7387fff5 100644
--- a/src/core/include/mp-units/bits/external/fixed_string.h
+++ b/src/core/include/mp-units/ext/fixed_string.h
@@ -23,13 +23,13 @@
 #pragma once
 
 // TODO use <algorithm> when moved to C++20 modules (parsing takes too long for each translation unit)
-#include <mp-units/bits/external/algorithm.h>
 #include <mp-units/bits/module_macros.h>
 #include <mp-units/compat_macros.h>  // IWYU pragma: keep
+#include <mp-units/ext/algorithm.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <gsl/gsl-lite.hpp>
-#include <compare>
+#include <compare>  // IWYU pragma: export
 #include <cstddef>
 #include <cstdlib>
 #include <ostream>
diff --git a/src/core/include/mp-units/bits/external/prime.h b/src/core/include/mp-units/ext/prime.h
similarity index 99%
rename from src/core/include/mp-units/bits/external/prime.h
rename to src/core/include/mp-units/ext/prime.h
index 06d03dde..9e0baa08 100644
--- a/src/core/include/mp-units/bits/external/prime.h
+++ b/src/core/include/mp-units/ext/prime.h
@@ -22,7 +22,7 @@
 
 #pragma once
 
-#include <mp-units/bits/external/algorithm.h>
+#include <mp-units/ext/algorithm.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <array>
diff --git a/src/core/include/mp-units/bits/external/type_name.h b/src/core/include/mp-units/ext/type_name.h
similarity index 100%
rename from src/core/include/mp-units/bits/external/type_name.h
rename to src/core/include/mp-units/ext/type_name.h
diff --git a/src/core/include/mp-units/bits/external/type_traits.h b/src/core/include/mp-units/ext/type_traits.h
similarity index 99%
rename from src/core/include/mp-units/bits/external/type_traits.h
rename to src/core/include/mp-units/ext/type_traits.h
index 3322a790..244ae160 100644
--- a/src/core/include/mp-units/bits/external/type_traits.h
+++ b/src/core/include/mp-units/ext/type_traits.h
@@ -22,7 +22,7 @@
 
 #pragma once
 
-#include <mp-units/bits/external/hacks.h>
+#include <mp-units/bits/hacks.h>
 #include <mp-units/bits/module_macros.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
diff --git a/src/core/include/mp-units/format.h b/src/core/include/mp-units/format.h
index f3ff7e50..44cda221 100644
--- a/src/core/include/mp-units/format.h
+++ b/src/core/include/mp-units/format.h
@@ -20,14 +20,16 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
+// IWYU pragma: always_keep
+
 #pragma once
 
-#include <mp-units/bits/external/algorithm.h>
 #include <mp-units/bits/fmt.h>
 #include <mp-units/compat_macros.h>
-#include <mp-units/customization_points.h>
-#include <mp-units/quantity.h>
-#include <mp-units/unit.h>
+#include <mp-units/ext/algorithm.h>
+#include <mp-units/framework/customization_points.h>
+#include <mp-units/framework/quantity.h>
+#include <mp-units/framework/unit.h>
 
 namespace mp_units::detail {
 
diff --git a/src/core/include/mp-units/framework.h b/src/core/include/mp-units/framework.h
new file mode 100644
index 00000000..7a61d351
--- /dev/null
+++ b/src/core/include/mp-units/framework.h
@@ -0,0 +1,46 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2018 Mateusz Pusz
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+#pragma once
+
+// IWYU pragma: begin_exports
+#include <mp-units/framework/compare.h>
+#include <mp-units/framework/customization_points.h>
+#include <mp-units/framework/dimension.h>
+#include <mp-units/framework/dimension_concepts.h>
+#include <mp-units/framework/expression_template.h>
+#include <mp-units/framework/magnitude.h>
+#include <mp-units/framework/quantity.h>
+#include <mp-units/framework/quantity_cast.h>
+#include <mp-units/framework/quantity_concepts.h>
+#include <mp-units/framework/quantity_point.h>
+#include <mp-units/framework/quantity_point_concepts.h>
+#include <mp-units/framework/quantity_spec.h>
+#include <mp-units/framework/quantity_spec_concepts.h>
+#include <mp-units/framework/reference.h>
+#include <mp-units/framework/representation_concepts.h>
+#include <mp-units/framework/symbol_text.h>
+#include <mp-units/framework/system_reference.h>
+#include <mp-units/framework/unit.h>
+#include <mp-units/framework/unit_concepts.h>
+#include <mp-units/framework/value_cast.h>
+// IWYU pragma: end_exports
diff --git a/src/core/include/mp-units/compare.h b/src/core/include/mp-units/framework/compare.h
similarity index 97%
rename from src/core/include/mp-units/compare.h
rename to src/core/include/mp-units/framework/compare.h
index e2fb0deb..718e9c55 100644
--- a/src/core/include/mp-units/compare.h
+++ b/src/core/include/mp-units/framework/compare.h
@@ -22,6 +22,7 @@
 
 #pragma once
 
+// IWYU pragma: private, include <mp-units/framework.h>
 #include <mp-units/bits/module_macros.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
diff --git a/src/core/include/mp-units/customization_points.h b/src/core/include/mp-units/framework/customization_points.h
similarity index 98%
rename from src/core/include/mp-units/customization_points.h
rename to src/core/include/mp-units/framework/customization_points.h
index 99578ea4..4e19ae27 100644
--- a/src/core/include/mp-units/customization_points.h
+++ b/src/core/include/mp-units/framework/customization_points.h
@@ -22,8 +22,9 @@
 
 #pragma once
 
-#include <mp-units/bits/external/type_traits.h>
+// IWYU pragma: private, include <mp-units/framework.h>
 #include <mp-units/bits/module_macros.h>
+#include <mp-units/ext/type_traits.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <limits>
diff --git a/src/core/include/mp-units/dimension.h b/src/core/include/mp-units/framework/dimension.h
similarity index 97%
rename from src/core/include/mp-units/dimension.h
rename to src/core/include/mp-units/framework/dimension.h
index ae5d233d..55968c4a 100644
--- a/src/core/include/mp-units/dimension.h
+++ b/src/core/include/mp-units/framework/dimension.h
@@ -22,13 +22,15 @@
 
 #pragma once
 
-#include <mp-units/bits/dimension_concepts.h>
-#include <mp-units/bits/expression_template.h>
-#include <mp-units/bits/external/hacks.h>
-#include <mp-units/bits/external/type_traits.h>
+// IWYU pragma: private, include <mp-units/framework.h>
+#include <mp-units/bits/hacks.h>
 #include <mp-units/bits/module_macros.h>
-#include <mp-units/bits/symbol_text.h>
 #include <mp-units/bits/text_tools.h>
+#include <mp-units/ext/fixed_string.h>
+#include <mp-units/ext/type_traits.h>
+#include <mp-units/framework/dimension_concepts.h>
+#include <mp-units/framework/expression_template.h>
+#include <mp-units/framework/symbol_text.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <gsl/gsl-lite.hpp>
diff --git a/src/core/include/mp-units/bits/dimension_concepts.h b/src/core/include/mp-units/framework/dimension_concepts.h
similarity index 95%
rename from src/core/include/mp-units/bits/dimension_concepts.h
rename to src/core/include/mp-units/framework/dimension_concepts.h
index b458ae5f..9826e1b0 100644
--- a/src/core/include/mp-units/bits/dimension_concepts.h
+++ b/src/core/include/mp-units/framework/dimension_concepts.h
@@ -22,10 +22,11 @@
 
 #pragma once
 
-#include <mp-units/bits/expression_template.h>
-#include <mp-units/bits/external/type_traits.h>
+// IWYU pragma: private, include <mp-units/framework.h>
 #include <mp-units/bits/module_macros.h>
-#include <mp-units/bits/symbol_text.h>
+#include <mp-units/ext/type_traits.h>
+#include <mp-units/framework/expression_template.h>
+#include <mp-units/framework/symbol_text.h>
 
 namespace mp_units {
 
diff --git a/src/core/include/mp-units/bits/expression_template.h b/src/core/include/mp-units/framework/expression_template.h
similarity index 99%
rename from src/core/include/mp-units/bits/expression_template.h
rename to src/core/include/mp-units/framework/expression_template.h
index 5ee18b62..c0eddbda 100644
--- a/src/core/include/mp-units/bits/expression_template.h
+++ b/src/core/include/mp-units/framework/expression_template.h
@@ -22,10 +22,10 @@
 
 #pragma once
 
-#include <mp-units/bits/external/math_concepts.h>
-#include <mp-units/bits/external/type_list.h>
-#include <mp-units/bits/external/type_traits.h>
+#include <mp-units/bits/math_concepts.h>
 #include <mp-units/bits/ratio.h>
+#include <mp-units/bits/type_list.h>
+#include <mp-units/ext/type_traits.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <cstdint>
diff --git a/src/core/include/mp-units/bits/magnitude.h b/src/core/include/mp-units/framework/magnitude.h
similarity index 98%
rename from src/core/include/mp-units/bits/magnitude.h
rename to src/core/include/mp-units/framework/magnitude.h
index 9a3f1cb1..29be6d88 100644
--- a/src/core/include/mp-units/bits/magnitude.h
+++ b/src/core/include/mp-units/framework/magnitude.h
@@ -22,17 +22,18 @@
 
 #pragma once
 
-#include <mp-units/bits/expression_template.h>
-#include <mp-units/bits/external/hacks.h>
-#include <mp-units/bits/external/math_concepts.h>
-#include <mp-units/bits/external/prime.h>
-#include <mp-units/bits/external/type_name.h>
-#include <mp-units/bits/external/type_traits.h>
+// IWYU pragma: private, include <mp-units/framework.h>
+#include <mp-units/bits/hacks.h>
+#include <mp-units/bits/math_concepts.h>
 #include <mp-units/bits/module_macros.h>
 #include <mp-units/bits/ratio.h>
-#include <mp-units/bits/symbol_text.h>
 #include <mp-units/bits/text_tools.h>
-#include <mp-units/customization_points.h>
+#include <mp-units/ext/prime.h>
+#include <mp-units/ext/type_name.h>
+#include <mp-units/ext/type_traits.h>
+#include <mp-units/framework/customization_points.h>
+#include <mp-units/framework/expression_template.h>
+#include <mp-units/framework/symbol_text.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <concepts>
diff --git a/src/core/include/mp-units/quantity.h b/src/core/include/mp-units/framework/quantity.h
similarity index 97%
rename from src/core/include/mp-units/quantity.h
rename to src/core/include/mp-units/framework/quantity.h
index 176cccc4..e759a86f 100644
--- a/src/core/include/mp-units/quantity.h
+++ b/src/core/include/mp-units/framework/quantity.h
@@ -23,27 +23,24 @@
 
 #pragma once
 
-#include <mp-units/bits/dimension_concepts.h>
+// IWYU pragma: private, include <mp-units/framework.h>
 #include <mp-units/bits/module_macros.h>
-#include <mp-units/bits/quantity_concepts.h>
-#include <mp-units/bits/quantity_spec_concepts.h>
-#include <mp-units/bits/reference_concepts.h>
-#include <mp-units/bits/representation_concepts.h>
 #include <mp-units/bits/sudo_cast.h>
-#include <mp-units/bits/unit_concepts.h>
-#include <mp-units/customization_points.h>
-#include <mp-units/reference.h>
+#include <mp-units/framework/customization_points.h>
+#include <mp-units/framework/dimension_concepts.h>
+#include <mp-units/framework/quantity_concepts.h>
+#include <mp-units/framework/quantity_spec_concepts.h>
+#include <mp-units/framework/reference.h>
+#include <mp-units/framework/reference_concepts.h>
+#include <mp-units/framework/representation_concepts.h>
+#include <mp-units/framework/unit_concepts.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <gsl/gsl-lite.hpp>
-#include <compare>
+#include <compare>  // IWYU pragma: export
 #include <utility>
 #endif
 
-// the below is not used in this header but should be exposed with it
-#include <mp-units/bits/quantity_cast.h>
-#include <mp-units/bits/value_cast.h>
-
 namespace mp_units {
 
 namespace detail {
diff --git a/src/core/include/mp-units/bits/quantity_cast.h b/src/core/include/mp-units/framework/quantity_cast.h
similarity index 93%
rename from src/core/include/mp-units/bits/quantity_cast.h
rename to src/core/include/mp-units/framework/quantity_cast.h
index 0f1c30af..64d0154b 100644
--- a/src/core/include/mp-units/bits/quantity_cast.h
+++ b/src/core/include/mp-units/framework/quantity_cast.h
@@ -22,10 +22,11 @@
 
 #pragma once
 
+// IWYU pragma: private, include <mp-units/framework.h>
 #include <mp-units/bits/module_macros.h>
-#include <mp-units/bits/quantity_concepts.h>
-#include <mp-units/bits/quantity_point_concepts.h>
-#include <mp-units/reference.h>
+#include <mp-units/framework/quantity_concepts.h>
+#include <mp-units/framework/quantity_point_concepts.h>
+#include <mp-units/framework/reference.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <type_traits>
diff --git a/src/core/include/mp-units/bits/quantity_concepts.h b/src/core/include/mp-units/framework/quantity_concepts.h
similarity index 92%
rename from src/core/include/mp-units/bits/quantity_concepts.h
rename to src/core/include/mp-units/framework/quantity_concepts.h
index 4b7e9aef..6886b8a9 100644
--- a/src/core/include/mp-units/bits/quantity_concepts.h
+++ b/src/core/include/mp-units/framework/quantity_concepts.h
@@ -22,11 +22,12 @@
 
 #pragma once
 
+// IWYU pragma: private, include <mp-units/framework.h>
 #include <mp-units/bits/module_macros.h>
-#include <mp-units/bits/quantity_spec_concepts.h>
-#include <mp-units/bits/reference_concepts.h>
-#include <mp-units/bits/representation_concepts.h>
-#include <mp-units/customization_points.h>
+#include <mp-units/framework/customization_points.h>
+#include <mp-units/framework/quantity_spec_concepts.h>
+#include <mp-units/framework/reference_concepts.h>
+#include <mp-units/framework/representation_concepts.h>
 
 namespace mp_units {
 
diff --git a/src/core/include/mp-units/quantity_point.h b/src/core/include/mp-units/framework/quantity_point.h
similarity index 98%
rename from src/core/include/mp-units/quantity_point.h
rename to src/core/include/mp-units/framework/quantity_point.h
index 19cb1d43..5b6699e3 100644
--- a/src/core/include/mp-units/quantity_point.h
+++ b/src/core/include/mp-units/framework/quantity_point.h
@@ -22,14 +22,15 @@
 
 #pragma once
 
+// IWYU pragma: private, include <mp-units/framework.h>
 #include <mp-units/bits/module_macros.h>
-#include <mp-units/bits/quantity_point_concepts.h>
-#include <mp-units/compare.h>
-#include <mp-units/customization_points.h>
-#include <mp-units/quantity.h>
+#include <mp-units/framework/compare.h>
+#include <mp-units/framework/customization_points.h>
+#include <mp-units/framework/quantity.h>
+#include <mp-units/framework/quantity_point_concepts.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
-#include <compare>
+#include <compare>  // IWYU pragma: export
 #endif
 
 namespace mp_units {
diff --git a/src/core/include/mp-units/bits/quantity_point_concepts.h b/src/core/include/mp-units/framework/quantity_point_concepts.h
similarity index 95%
rename from src/core/include/mp-units/bits/quantity_point_concepts.h
rename to src/core/include/mp-units/framework/quantity_point_concepts.h
index 0a2cc8fc..ee5ca8eb 100644
--- a/src/core/include/mp-units/bits/quantity_point_concepts.h
+++ b/src/core/include/mp-units/framework/quantity_point_concepts.h
@@ -22,12 +22,13 @@
 
 #pragma once
 
+// IWYU pragma: private, include <mp-units/framework.h>
 #include <mp-units/bits/module_macros.h>
-#include <mp-units/bits/quantity_concepts.h>
-#include <mp-units/bits/quantity_spec_concepts.h>
-#include <mp-units/bits/reference_concepts.h>
-#include <mp-units/bits/representation_concepts.h>
-#include <mp-units/customization_points.h>
+#include <mp-units/framework/customization_points.h>
+#include <mp-units/framework/quantity_concepts.h>
+#include <mp-units/framework/quantity_spec_concepts.h>
+#include <mp-units/framework/reference_concepts.h>
+#include <mp-units/framework/representation_concepts.h>
 
 namespace mp_units {
 
diff --git a/src/core/include/mp-units/quantity_spec.h b/src/core/include/mp-units/framework/quantity_spec.h
similarity index 99%
rename from src/core/include/mp-units/quantity_spec.h
rename to src/core/include/mp-units/framework/quantity_spec.h
index 5d091b41..bbd4941c 100644
--- a/src/core/include/mp-units/quantity_spec.h
+++ b/src/core/include/mp-units/framework/quantity_spec.h
@@ -22,19 +22,20 @@
 
 #pragma once
 
-#include <mp-units/bits/expression_template.h>
-#include <mp-units/bits/external/algorithm.h>
-#include <mp-units/bits/external/hacks.h>
-#include <mp-units/bits/external/type_name.h>
-#include <mp-units/bits/external/type_traits.h>
+// IWYU pragma: private, include <mp-units/framework.h>
 #include <mp-units/bits/get_common_base.h>
+#include <mp-units/bits/hacks.h>
 #include <mp-units/bits/module_macros.h>
-#include <mp-units/bits/quantity_concepts.h>
-#include <mp-units/bits/quantity_spec_concepts.h>
-#include <mp-units/bits/reference_concepts.h>
-#include <mp-units/bits/representation_concepts.h>
 #include <mp-units/compat_macros.h>
-#include <mp-units/dimension.h>
+#include <mp-units/ext/algorithm.h>
+#include <mp-units/ext/type_name.h>
+#include <mp-units/ext/type_traits.h>
+#include <mp-units/framework/dimension.h>
+#include <mp-units/framework/expression_template.h>
+#include <mp-units/framework/quantity_concepts.h>
+#include <mp-units/framework/quantity_spec_concepts.h>
+#include <mp-units/framework/reference_concepts.h>
+#include <mp-units/framework/representation_concepts.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <cstdint>
diff --git a/src/core/include/mp-units/bits/quantity_spec_concepts.h b/src/core/include/mp-units/framework/quantity_spec_concepts.h
similarity index 96%
rename from src/core/include/mp-units/bits/quantity_spec_concepts.h
rename to src/core/include/mp-units/framework/quantity_spec_concepts.h
index d04e8bd7..920e9cf5 100644
--- a/src/core/include/mp-units/bits/quantity_spec_concepts.h
+++ b/src/core/include/mp-units/framework/quantity_spec_concepts.h
@@ -22,10 +22,11 @@
 
 #pragma once
 
-#include <mp-units/bits/dimension_concepts.h>
-#include <mp-units/bits/expression_template.h>
-#include <mp-units/bits/external/hacks.h>
+// IWYU pragma: private, include <mp-units/framework.h>
+#include <mp-units/bits/hacks.h>
 #include <mp-units/bits/module_macros.h>
+#include <mp-units/framework/dimension_concepts.h>
+#include <mp-units/framework/expression_template.h>
 
 namespace mp_units {
 
diff --git a/src/core/include/mp-units/reference.h b/src/core/include/mp-units/framework/reference.h
similarity index 97%
rename from src/core/include/mp-units/reference.h
rename to src/core/include/mp-units/framework/reference.h
index 7b37c4e9..b7636810 100644
--- a/src/core/include/mp-units/reference.h
+++ b/src/core/include/mp-units/framework/reference.h
@@ -22,11 +22,12 @@
 
 #pragma once
 
+// IWYU pragma: private, include <mp-units/framework.h>
 #include <mp-units/bits/get_associated_quantity.h>
 #include <mp-units/bits/module_macros.h>
-#include <mp-units/bits/quantity_concepts.h>
-#include <mp-units/bits/reference_concepts.h>
-#include <mp-units/bits/representation_concepts.h>
+#include <mp-units/framework/quantity_concepts.h>
+#include <mp-units/framework/reference_concepts.h>
+#include <mp-units/framework/representation_concepts.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <cstdint>
diff --git a/src/core/include/mp-units/bits/reference_concepts.h b/src/core/include/mp-units/framework/reference_concepts.h
similarity index 94%
rename from src/core/include/mp-units/bits/reference_concepts.h
rename to src/core/include/mp-units/framework/reference_concepts.h
index 639fcbca..6ac2187b 100644
--- a/src/core/include/mp-units/bits/reference_concepts.h
+++ b/src/core/include/mp-units/framework/reference_concepts.h
@@ -22,9 +22,10 @@
 
 #pragma once
 
+// IWYU pragma: private, include <mp-units/framework.h>
 #include <mp-units/bits/module_macros.h>
-#include <mp-units/bits/quantity_spec_concepts.h>
-#include <mp-units/bits/unit_concepts.h>
+#include <mp-units/framework/quantity_spec_concepts.h>
+#include <mp-units/framework/unit_concepts.h>
 
 namespace mp_units {
 
diff --git a/src/core/include/mp-units/bits/representation_concepts.h b/src/core/include/mp-units/framework/representation_concepts.h
similarity index 97%
rename from src/core/include/mp-units/bits/representation_concepts.h
rename to src/core/include/mp-units/framework/representation_concepts.h
index 9f9bfa52..3528eea4 100644
--- a/src/core/include/mp-units/bits/representation_concepts.h
+++ b/src/core/include/mp-units/framework/representation_concepts.h
@@ -22,8 +22,9 @@
 
 #pragma once
 
+// IWYU pragma: private, include <mp-units/framework.h>
 #include <mp-units/bits/module_macros.h>
-#include <mp-units/customization_points.h>
+#include <mp-units/framework/customization_points.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <concepts>
diff --git a/src/core/include/mp-units/bits/symbol_text.h b/src/core/include/mp-units/framework/symbol_text.h
similarity index 93%
rename from src/core/include/mp-units/bits/symbol_text.h
rename to src/core/include/mp-units/framework/symbol_text.h
index e28d4cde..b70b3d2f 100644
--- a/src/core/include/mp-units/bits/symbol_text.h
+++ b/src/core/include/mp-units/framework/symbol_text.h
@@ -22,15 +22,16 @@
 
 #pragma once
 
-// IWYU pragma: begin_exports
-#include <mp-units/bits/external/fixed_string.h>
-#include <mp-units/bits/external/hacks.h>
+// IWYU pragma: private, include <mp-units/framework.h>
+#include <mp-units/bits/hacks.h>
 #include <mp-units/bits/module_macros.h>
+#include <mp-units/ext/fixed_string.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <gsl/gsl-lite.hpp>
-#include <compare>
+#include <compare>  // IWYU pragma: export
 #include <cstddef>
+#include <cstdint>
 #endif
 
 #if __cpp_lib_text_encoding
@@ -42,6 +43,12 @@ static_assert(std::text_encoding::literal().mib() == std::text_encoding::id::UTF
 
 namespace mp_units {
 
+MP_UNITS_EXPORT enum class text_encoding : std::int8_t {
+  unicode,  // µs; m³;  L²MT⁻³
+  ascii,    // us; m^3; L^2MT^-3
+  default_encoding = unicode
+};
+
 namespace detail {
 
 constexpr bool is_basic_literal_character_set_char(char ch)
diff --git a/src/core/include/mp-units/system_reference.h b/src/core/include/mp-units/framework/system_reference.h
similarity index 93%
rename from src/core/include/mp-units/system_reference.h
rename to src/core/include/mp-units/framework/system_reference.h
index 7bf30383..39f16bcf 100644
--- a/src/core/include/mp-units/system_reference.h
+++ b/src/core/include/mp-units/framework/system_reference.h
@@ -22,11 +22,12 @@
 
 #pragma once
 
-#include <mp-units/bits/external/hacks.h>
+// IWYU pragma: private, include <mp-units/framework.h>
+#include <mp-units/bits/hacks.h>
 #include <mp-units/bits/module_macros.h>
-#include <mp-units/quantity_spec.h>
-#include <mp-units/reference.h>
-#include <mp-units/unit.h>
+#include <mp-units/framework/quantity_spec.h>
+#include <mp-units/framework/reference.h>
+#include <mp-units/framework/unit.h>
 
 MP_UNITS_EXPORT
 namespace mp_units {
diff --git a/src/core/include/mp-units/unit.h b/src/core/include/mp-units/framework/unit.h
similarity index 98%
rename from src/core/include/mp-units/unit.h
rename to src/core/include/mp-units/framework/unit.h
index b703d9e1..16d89822 100644
--- a/src/core/include/mp-units/unit.h
+++ b/src/core/include/mp-units/framework/unit.h
@@ -22,21 +22,22 @@
 
 #pragma once
 
-#include <mp-units/bits/expression_template.h>
-#include <mp-units/bits/external/algorithm.h>
-#include <mp-units/bits/external/fixed_string.h>
-#include <mp-units/bits/external/hacks.h>
-#include <mp-units/bits/external/type_name.h>
-#include <mp-units/bits/external/type_traits.h>
+// IWYU pragma: private, include <mp-units/framework.h>
 #include <mp-units/bits/get_associated_quantity.h>
-#include <mp-units/bits/magnitude.h>
+#include <mp-units/bits/hacks.h>
 #include <mp-units/bits/module_macros.h>
-#include <mp-units/bits/quantity_point_concepts.h>
-#include <mp-units/bits/quantity_spec_concepts.h>
 #include <mp-units/bits/ratio.h>
-#include <mp-units/bits/symbol_text.h>
 #include <mp-units/bits/text_tools.h>
-#include <mp-units/bits/unit_concepts.h>
+#include <mp-units/ext/algorithm.h>
+#include <mp-units/ext/fixed_string.h>
+#include <mp-units/ext/type_name.h>
+#include <mp-units/ext/type_traits.h>
+#include <mp-units/framework/expression_template.h>
+#include <mp-units/framework/magnitude.h>
+#include <mp-units/framework/quantity_point_concepts.h>
+#include <mp-units/framework/quantity_spec_concepts.h>
+#include <mp-units/framework/symbol_text.h>
+#include <mp-units/framework/unit_concepts.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <gsl/gsl-lite.hpp>
diff --git a/src/core/include/mp-units/bits/unit_concepts.h b/src/core/include/mp-units/framework/unit_concepts.h
similarity index 96%
rename from src/core/include/mp-units/bits/unit_concepts.h
rename to src/core/include/mp-units/framework/unit_concepts.h
index 29331c7a..c536e0b4 100644
--- a/src/core/include/mp-units/bits/unit_concepts.h
+++ b/src/core/include/mp-units/framework/unit_concepts.h
@@ -22,11 +22,12 @@
 
 #pragma once
 
-#include <mp-units/bits/expression_template.h>
-#include <mp-units/bits/magnitude.h>
+// IWYU pragma: private, include <mp-units/framework.h>
 #include <mp-units/bits/module_macros.h>
-#include <mp-units/bits/quantity_spec_concepts.h>
-#include <mp-units/bits/symbol_text.h>
+#include <mp-units/framework/expression_template.h>
+#include <mp-units/framework/magnitude.h>
+#include <mp-units/framework/quantity_spec_concepts.h>
+#include <mp-units/framework/symbol_text.h>
 
 namespace mp_units {
 
diff --git a/src/core/include/mp-units/bits/value_cast.h b/src/core/include/mp-units/framework/value_cast.h
similarity index 95%
rename from src/core/include/mp-units/bits/value_cast.h
rename to src/core/include/mp-units/framework/value_cast.h
index 7b2c6ddd..eaedbd17 100644
--- a/src/core/include/mp-units/bits/value_cast.h
+++ b/src/core/include/mp-units/framework/value_cast.h
@@ -22,13 +22,14 @@
 
 #pragma once
 
+// IWYU pragma: private, include <mp-units/framework.h>
 #include <mp-units/bits/module_macros.h>
-#include <mp-units/bits/quantity_concepts.h>
-#include <mp-units/bits/quantity_point_concepts.h>
-#include <mp-units/bits/representation_concepts.h>
 #include <mp-units/bits/sudo_cast.h>
-#include <mp-units/bits/unit_concepts.h>
-#include <mp-units/reference.h>
+#include <mp-units/framework/quantity_concepts.h>
+#include <mp-units/framework/quantity_point_concepts.h>
+#include <mp-units/framework/reference.h>
+#include <mp-units/framework/representation_concepts.h>
+#include <mp-units/framework/unit_concepts.h>
 
 MP_UNITS_EXPORT
 namespace mp_units {
diff --git a/src/core/include/mp-units/math.h b/src/core/include/mp-units/math.h
index cbd6bc2b..90a6539a 100644
--- a/src/core/include/mp-units/math.h
+++ b/src/core/include/mp-units/math.h
@@ -23,10 +23,10 @@
 #pragma once
 
 #include <mp-units/bits/module_macros.h>
-#include <mp-units/bits/value_cast.h>
-#include <mp-units/customization_points.h>
-#include <mp-units/quantity.h>
-#include <mp-units/unit.h>
+#include <mp-units/framework/customization_points.h>
+#include <mp-units/framework/quantity.h>
+#include <mp-units/framework/unit.h>
+#include <mp-units/framework/value_cast.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <cmath>
diff --git a/src/core/include/mp-units/ostream.h b/src/core/include/mp-units/ostream.h
index 4b36b065..e03bb33c 100644
--- a/src/core/include/mp-units/ostream.h
+++ b/src/core/include/mp-units/ostream.h
@@ -24,8 +24,8 @@
 #pragma once
 
 #include <mp-units/bits/module_macros.h>
-#include <mp-units/quantity.h>
-#include <mp-units/unit.h>
+#include <mp-units/framework/quantity.h>
+#include <mp-units/framework/unit.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <cstdint>
diff --git a/src/core/include/mp-units/random.h b/src/core/include/mp-units/random.h
index b66cfb22..aa097e80 100644
--- a/src/core/include/mp-units/random.h
+++ b/src/core/include/mp-units/random.h
@@ -23,7 +23,7 @@
 #pragma once
 
 #include <mp-units/bits/module_macros.h>
-#include <mp-units/quantity.h>
+#include <mp-units/framework/quantity.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <functional>
diff --git a/src/systems/include/mp-units/systems/angular/angular.h b/src/systems/include/mp-units/systems/angular/angular.h
index e9461440..326ea227 100644
--- a/src/systems/include/mp-units/systems/angular/angular.h
+++ b/src/systems/include/mp-units/systems/angular/angular.h
@@ -22,5 +22,11 @@
 
 #pragma once
 
+// IWYU pragma: begin_exports
 #include <mp-units/systems/angular/math.h>
 #include <mp-units/systems/angular/units.h>
+
+#ifndef MP_UNITS_IN_MODULE_INTERFACE
+#include <mp-units/framework.h>
+#endif
+// IWYU pragma: end_exports
diff --git a/src/systems/include/mp-units/systems/angular/math.h b/src/systems/include/mp-units/systems/angular/math.h
index 63a2d8f3..00e03b7a 100644
--- a/src/systems/include/mp-units/systems/angular/math.h
+++ b/src/systems/include/mp-units/systems/angular/math.h
@@ -26,10 +26,10 @@
 #include <mp-units/systems/angular/units.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
-#include <mp-units/bits/value_cast.h>
-#include <mp-units/customization_points.h>
-#include <mp-units/quantity.h>
-#include <mp-units/unit.h>
+#include <mp-units/framework/customization_points.h>
+#include <mp-units/framework/quantity.h>
+#include <mp-units/framework/unit.h>
+#include <mp-units/framework/value_cast.h>
 #include <cmath>
 #endif
 
diff --git a/src/systems/include/mp-units/systems/angular/units.h b/src/systems/include/mp-units/systems/angular/units.h
index 0ca22c77..f0de3ead 100644
--- a/src/systems/include/mp-units/systems/angular/units.h
+++ b/src/systems/include/mp-units/systems/angular/units.h
@@ -25,9 +25,9 @@
 #include <mp-units/bits/module_macros.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
-#include <mp-units/dimension.h>
-#include <mp-units/quantity_spec.h>
-#include <mp-units/unit.h>
+#include <mp-units/framework/dimension.h>
+#include <mp-units/framework/quantity_spec.h>
+#include <mp-units/framework/unit.h>
 #endif
 
 MP_UNITS_EXPORT
diff --git a/src/systems/include/mp-units/systems/cgs/cgs.h b/src/systems/include/mp-units/systems/cgs/cgs.h
index ed7d4ccc..f3e58e54 100644
--- a/src/systems/include/mp-units/systems/cgs/cgs.h
+++ b/src/systems/include/mp-units/systems/cgs/cgs.h
@@ -25,9 +25,11 @@
 #include <mp-units/bits/module_macros.h>
 #include <mp-units/systems/si/units.h>
 
+// IWYU pragma: begin_exports
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
-#include <mp-units/unit.h>
+#include <mp-units/framework.h>
 #endif
+// IWYU pragma: end_exports
 
 MP_UNITS_EXPORT
 namespace mp_units::cgs {
diff --git a/src/systems/include/mp-units/systems/hep/hep.h b/src/systems/include/mp-units/systems/hep/hep.h
index a2dd17bf..bddb2822 100644
--- a/src/systems/include/mp-units/systems/hep/hep.h
+++ b/src/systems/include/mp-units/systems/hep/hep.h
@@ -24,11 +24,13 @@
 
 #include <mp-units/bits/module_macros.h>
 #include <mp-units/systems/si/si.h>
-
-#ifndef MP_UNITS_IN_MODULE_INTERFACE
-#include <mp-units/unit.h>
 #include <cstdint>
+
+// IWYU pragma: begin_exports
+#ifndef MP_UNITS_IN_MODULE_INTERFACE
+#include <mp-units/framework.h>
 #endif
+// IWYU pragma: end_exports
 
 MP_UNITS_EXPORT
 namespace mp_units {
diff --git a/src/systems/include/mp-units/systems/iau/iau.h b/src/systems/include/mp-units/systems/iau/iau.h
index bc4c50aa..abbe963d 100644
--- a/src/systems/include/mp-units/systems/iau/iau.h
+++ b/src/systems/include/mp-units/systems/iau/iau.h
@@ -26,9 +26,11 @@
 #include <mp-units/systems/si/constants.h>
 #include <mp-units/systems/si/units.h>
 
+// IWYU pragma: begin_exports
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
-#include <mp-units/unit.h>
+#include <mp-units/framework.h>
 #endif
+// IWYU pragma: end_exports
 
 MP_UNITS_EXPORT
 namespace mp_units::iau {
diff --git a/src/systems/include/mp-units/systems/iec80000/binary_prefixes.h b/src/systems/include/mp-units/systems/iec80000/binary_prefixes.h
index 65a2e498..bfcc9b4f 100644
--- a/src/systems/include/mp-units/systems/iec80000/binary_prefixes.h
+++ b/src/systems/include/mp-units/systems/iec80000/binary_prefixes.h
@@ -25,7 +25,7 @@
 #include <mp-units/bits/module_macros.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
-#include <mp-units/unit.h>
+#include <mp-units/framework/unit.h>
 #endif
 
 namespace mp_units::iec80000 {
diff --git a/src/systems/include/mp-units/systems/iec80000/iec80000.h b/src/systems/include/mp-units/systems/iec80000/iec80000.h
index 9fd164b7..0b19046b 100644
--- a/src/systems/include/mp-units/systems/iec80000/iec80000.h
+++ b/src/systems/include/mp-units/systems/iec80000/iec80000.h
@@ -27,4 +27,8 @@
 #include <mp-units/systems/iec80000/quantities.h>
 #include <mp-units/systems/iec80000/unit_symbols.h>
 #include <mp-units/systems/iec80000/units.h>
+
+#ifndef MP_UNITS_IN_MODULE_INTERFACE
+#include <mp-units/framework.h>
+#endif
 // IWYU pragma: end_exports
diff --git a/src/systems/include/mp-units/systems/iec80000/quantities.h b/src/systems/include/mp-units/systems/iec80000/quantities.h
index 1a8e319f..04f1191f 100644
--- a/src/systems/include/mp-units/systems/iec80000/quantities.h
+++ b/src/systems/include/mp-units/systems/iec80000/quantities.h
@@ -27,8 +27,8 @@
 #include <mp-units/systems/isq/space_and_time.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
-#include <mp-units/dimension.h>
-#include <mp-units/quantity_spec.h>
+#include <mp-units/framework/dimension.h>
+#include <mp-units/framework/quantity_spec.h>
 #endif
 
 MP_UNITS_EXPORT
diff --git a/src/systems/include/mp-units/systems/iec80000/units.h b/src/systems/include/mp-units/systems/iec80000/units.h
index c8ec5aeb..9dd80c38 100644
--- a/src/systems/include/mp-units/systems/iec80000/units.h
+++ b/src/systems/include/mp-units/systems/iec80000/units.h
@@ -27,7 +27,7 @@
 #include <mp-units/systems/si/units.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
-#include <mp-units/unit.h>
+#include <mp-units/framework/unit.h>
 #endif
 
 MP_UNITS_EXPORT
diff --git a/src/systems/include/mp-units/systems/imperial/imperial.h b/src/systems/include/mp-units/systems/imperial/imperial.h
index 0b21434e..56c232cb 100644
--- a/src/systems/include/mp-units/systems/imperial/imperial.h
+++ b/src/systems/include/mp-units/systems/imperial/imperial.h
@@ -23,11 +23,14 @@
 #pragma once
 
 #include <mp-units/bits/module_macros.h>
+
+// IWYU pragma: begin_exports
 #include <mp-units/systems/international/international.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
-#include <mp-units/unit.h>
+#include <mp-units/framework.h>
 #endif
+// IWYU pragma: end_exports
 
 MP_UNITS_EXPORT
 namespace mp_units::imperial {
diff --git a/src/systems/include/mp-units/systems/international/international.h b/src/systems/include/mp-units/systems/international/international.h
index ba37696f..0b680ce3 100644
--- a/src/systems/include/mp-units/systems/international/international.h
+++ b/src/systems/include/mp-units/systems/international/international.h
@@ -26,9 +26,11 @@
 #include <mp-units/systems/si/constants.h>
 #include <mp-units/systems/si/units.h>
 
+// IWYU pragma: begin_exports
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
-#include <mp-units/unit.h>
+#include <mp-units/framework.h>
 #endif
+// IWYU pragma: end_exports
 
 MP_UNITS_EXPORT
 namespace mp_units::international {
diff --git a/src/systems/include/mp-units/systems/isq/atomic_and_nuclear_physics.h b/src/systems/include/mp-units/systems/isq/atomic_and_nuclear_physics.h
index 7bc3ca10..f5d1afae 100644
--- a/src/systems/include/mp-units/systems/isq/atomic_and_nuclear_physics.h
+++ b/src/systems/include/mp-units/systems/isq/atomic_and_nuclear_physics.h
@@ -23,11 +23,14 @@
 #pragma once
 
 #include <mp-units/bits/module_macros.h>
+
+// IWYU pragma: begin_exports
 #include <mp-units/systems/isq/si_quantities.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
-#include <mp-units/quantity_spec.h>
+#include <mp-units/framework/quantity_spec.h>
 #endif
+// IWYU pragma: end_exports
 
 MP_UNITS_EXPORT
 namespace mp_units::isq {
diff --git a/src/systems/include/mp-units/systems/isq/base_quantities.h b/src/systems/include/mp-units/systems/isq/base_quantities.h
index 89bc15eb..6ed87f7c 100644
--- a/src/systems/include/mp-units/systems/isq/base_quantities.h
+++ b/src/systems/include/mp-units/systems/isq/base_quantities.h
@@ -25,9 +25,9 @@
 #include <mp-units/bits/module_macros.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
-#include <mp-units/dimension.h>
-#include <mp-units/quantity.h>
-#include <mp-units/quantity_spec.h>
+#include <mp-units/framework/dimension.h>
+#include <mp-units/framework/quantity.h>
+#include <mp-units/framework/quantity_spec.h>
 #endif
 
 MP_UNITS_EXPORT
diff --git a/src/systems/include/mp-units/systems/isq/electromagnetism.h b/src/systems/include/mp-units/systems/isq/electromagnetism.h
index c4722ec5..bdb5bc8b 100644
--- a/src/systems/include/mp-units/systems/isq/electromagnetism.h
+++ b/src/systems/include/mp-units/systems/isq/electromagnetism.h
@@ -23,13 +23,16 @@
 #pragma once
 
 #include <mp-units/bits/module_macros.h>
-#include <mp-units/systems/isq/base_quantities.h>
 #include <mp-units/systems/isq/mechanics.h>
 #include <mp-units/systems/isq/space_and_time.h>
 
+// IWYU pragma: begin_exports
+#include <mp-units/systems/isq/base_quantities.h>
+
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
-#include <mp-units/quantity_spec.h>
+#include <mp-units/framework/quantity_spec.h>
 #endif
+// IWYU pragma: end_exports
 
 MP_UNITS_EXPORT
 namespace mp_units::isq {
diff --git a/src/systems/include/mp-units/systems/isq/light_and_radiation.h b/src/systems/include/mp-units/systems/isq/light_and_radiation.h
index b558a12b..bfca2dbf 100644
--- a/src/systems/include/mp-units/systems/isq/light_and_radiation.h
+++ b/src/systems/include/mp-units/systems/isq/light_and_radiation.h
@@ -23,13 +23,16 @@
 #pragma once
 
 #include <mp-units/bits/module_macros.h>
-#include <mp-units/systems/isq/base_quantities.h>
 #include <mp-units/systems/isq/electromagnetism.h>
 #include <mp-units/systems/isq/space_and_time.h>
 
+// IWYU pragma: begin_exports
+#include <mp-units/systems/isq/base_quantities.h>
+
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
-#include <mp-units/quantity_spec.h>
+#include <mp-units/framework/quantity_spec.h>
 #endif
+// IWYU pragma: end_exports
 
 MP_UNITS_EXPORT
 namespace mp_units::isq {
diff --git a/src/systems/include/mp-units/systems/isq/mechanics.h b/src/systems/include/mp-units/systems/isq/mechanics.h
index 95e90a98..41157143 100644
--- a/src/systems/include/mp-units/systems/isq/mechanics.h
+++ b/src/systems/include/mp-units/systems/isq/mechanics.h
@@ -23,12 +23,15 @@
 #pragma once
 
 #include <mp-units/bits/module_macros.h>
-#include <mp-units/systems/isq/si_quantities.h>
 #include <mp-units/systems/isq/space_and_time.h>
 
+// IWYU pragma: begin_exports
+#include <mp-units/systems/isq/si_quantities.h>
+
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
-#include <mp-units/quantity_spec.h>
+#include <mp-units/framework/quantity_spec.h>
 #endif
+// IWYU pragma: end_exports
 
 MP_UNITS_EXPORT
 namespace mp_units::isq {
diff --git a/src/systems/include/mp-units/systems/isq/si_quantities.h b/src/systems/include/mp-units/systems/isq/si_quantities.h
index 3d42bd53..9486c3e3 100644
--- a/src/systems/include/mp-units/systems/isq/si_quantities.h
+++ b/src/systems/include/mp-units/systems/isq/si_quantities.h
@@ -23,11 +23,14 @@
 #pragma once
 
 #include <mp-units/bits/module_macros.h>
+
+// IWYU pragma: begin_exports
 #include <mp-units/systems/isq/base_quantities.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
-#include <mp-units/quantity_spec.h>
+#include <mp-units/framework/quantity_spec.h>
 #endif
+// IWYU pragma: end_exports
 
 MP_UNITS_EXPORT
 namespace mp_units::isq {
diff --git a/src/systems/include/mp-units/systems/isq/space_and_time.h b/src/systems/include/mp-units/systems/isq/space_and_time.h
index e72cb9eb..2157a299 100644
--- a/src/systems/include/mp-units/systems/isq/space_and_time.h
+++ b/src/systems/include/mp-units/systems/isq/space_and_time.h
@@ -23,11 +23,14 @@
 #pragma once
 
 #include <mp-units/bits/module_macros.h>
+
+// IWYU pragma: begin_exports
 #include <mp-units/systems/isq/si_quantities.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
-#include <mp-units/quantity_spec.h>
+#include <mp-units/framework/quantity_spec.h>
 #endif
+// IWYU pragma: end_exports
 
 MP_UNITS_EXPORT
 namespace mp_units::isq {
diff --git a/src/systems/include/mp-units/systems/isq/thermodynamics.h b/src/systems/include/mp-units/systems/isq/thermodynamics.h
index 75743e31..aed8edf9 100644
--- a/src/systems/include/mp-units/systems/isq/thermodynamics.h
+++ b/src/systems/include/mp-units/systems/isq/thermodynamics.h
@@ -24,12 +24,15 @@
 
 #include <mp-units/bits/module_macros.h>
 #include <mp-units/systems/isq/mechanics.h>
-#include <mp-units/systems/isq/si_quantities.h>
 #include <mp-units/systems/isq/space_and_time.h>
 
+// IWYU pragma: begin_exports
+#include <mp-units/systems/isq/si_quantities.h>
+
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
-#include <mp-units/quantity_spec.h>
+#include <mp-units/framework/quantity_spec.h>
 #endif
+// IWYU pragma: end_exports
 
 MP_UNITS_EXPORT
 namespace mp_units::isq {
diff --git a/src/systems/include/mp-units/systems/isq_angle/isq_angle.h b/src/systems/include/mp-units/systems/isq_angle/isq_angle.h
index 2b4db46c..221719e7 100644
--- a/src/systems/include/mp-units/systems/isq_angle/isq_angle.h
+++ b/src/systems/include/mp-units/systems/isq_angle/isq_angle.h
@@ -23,13 +23,16 @@
 #pragma once
 
 #include <mp-units/bits/module_macros.h>
+
+// IWYU pragma: begin_exports
 #include <mp-units/systems/angular/angular.h>
 #include <mp-units/systems/isq/isq.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
-#include <mp-units/quantity_spec.h>
-#include <mp-units/reference.h>
+#include <mp-units/framework/quantity_spec.h>
+#include <mp-units/framework/reference.h>
 #endif
+// IWYU pragma: end_exports
 
 MP_UNITS_EXPORT
 namespace mp_units::isq_angle {
diff --git a/src/systems/include/mp-units/systems/natural/natural.h b/src/systems/include/mp-units/systems/natural/natural.h
index 0b534cbf..b56ee725 100644
--- a/src/systems/include/mp-units/systems/natural/natural.h
+++ b/src/systems/include/mp-units/systems/natural/natural.h
@@ -27,10 +27,11 @@
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/si/prefixes.h>
 
+// IWYU pragma: begin_exports
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
-#include <mp-units/system_reference.h>
-#include <mp-units/unit.h>
+#include <mp-units/framework.h>
 #endif
+// IWYU pragma: end_exports
 
 MP_UNITS_EXPORT
 namespace mp_units::natural {
diff --git a/src/systems/include/mp-units/systems/si/chrono.h b/src/systems/include/mp-units/systems/si/chrono.h
index 7e7c87e7..b8bcc589 100644
--- a/src/systems/include/mp-units/systems/si/chrono.h
+++ b/src/systems/include/mp-units/systems/si/chrono.h
@@ -28,8 +28,8 @@
 #include <mp-units/systems/si/units.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
-#include <mp-units/customization_points.h>
-#include <mp-units/quantity_point.h>
+#include <mp-units/framework/customization_points.h>
+#include <mp-units/framework/quantity_point.h>
 #include <chrono>
 #endif
 
diff --git a/src/systems/include/mp-units/systems/si/constants.h b/src/systems/include/mp-units/systems/si/constants.h
index 87ad4012..6f4afef6 100644
--- a/src/systems/include/mp-units/systems/si/constants.h
+++ b/src/systems/include/mp-units/systems/si/constants.h
@@ -26,7 +26,7 @@
 #include <mp-units/systems/si/units.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
-#include <mp-units/quantity.h>
+#include <mp-units/framework/quantity.h>
 #endif
 
 MP_UNITS_EXPORT
diff --git a/src/systems/include/mp-units/systems/si/math.h b/src/systems/include/mp-units/systems/si/math.h
index 371fb2f5..400a5a25 100644
--- a/src/systems/include/mp-units/systems/si/math.h
+++ b/src/systems/include/mp-units/systems/si/math.h
@@ -27,10 +27,10 @@
 #include <mp-units/systems/si/units.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
-#include <mp-units/bits/value_cast.h>
-#include <mp-units/customization_points.h>
-#include <mp-units/quantity.h>
-#include <mp-units/unit.h>
+#include <mp-units/framework/customization_points.h>
+#include <mp-units/framework/quantity.h>
+#include <mp-units/framework/unit.h>
+#include <mp-units/framework/value_cast.h>
 #include <cmath>
 #endif
 
diff --git a/src/systems/include/mp-units/systems/si/prefixes.h b/src/systems/include/mp-units/systems/si/prefixes.h
index 69077888..da2fb5b7 100644
--- a/src/systems/include/mp-units/systems/si/prefixes.h
+++ b/src/systems/include/mp-units/systems/si/prefixes.h
@@ -25,7 +25,7 @@
 #include <mp-units/bits/module_macros.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
-#include <mp-units/unit.h>
+#include <mp-units/framework/unit.h>
 #endif
 
 namespace mp_units::si {
diff --git a/src/systems/include/mp-units/systems/si/si.h b/src/systems/include/mp-units/systems/si/si.h
index b2668de5..b9b374d7 100644
--- a/src/systems/include/mp-units/systems/si/si.h
+++ b/src/systems/include/mp-units/systems/si/si.h
@@ -22,9 +22,15 @@
 
 #pragma once
 
+// IWYU pragma: begin_exports
 #include <mp-units/systems/si/chrono.h>
 #include <mp-units/systems/si/constants.h>
 #include <mp-units/systems/si/math.h>
 #include <mp-units/systems/si/prefixes.h>
 #include <mp-units/systems/si/unit_symbols.h>
 #include <mp-units/systems/si/units.h>
+
+#ifndef MP_UNITS_IN_MODULE_INTERFACE
+#include <mp-units/framework.h>
+#endif
+// IWYU pragma: end_exports
diff --git a/src/systems/include/mp-units/systems/si/units.h b/src/systems/include/mp-units/systems/si/units.h
index 360028e0..36d7772f 100644
--- a/src/systems/include/mp-units/systems/si/units.h
+++ b/src/systems/include/mp-units/systems/si/units.h
@@ -27,8 +27,8 @@
 #include <mp-units/systems/si/prefixes.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
-#include <mp-units/quantity_point.h>
-#include <mp-units/unit.h>
+#include <mp-units/framework/quantity_point.h>
+#include <mp-units/framework/unit.h>
 #endif
 
 MP_UNITS_EXPORT
diff --git a/src/systems/include/mp-units/systems/typographic/typographic.h b/src/systems/include/mp-units/systems/typographic/typographic.h
index 82186177..8f2b8563 100644
--- a/src/systems/include/mp-units/systems/typographic/typographic.h
+++ b/src/systems/include/mp-units/systems/typographic/typographic.h
@@ -25,9 +25,11 @@
 #include <mp-units/bits/module_macros.h>
 #include <mp-units/systems/international/international.h>
 
+// IWYU pragma: begin_exports
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
-#include <mp-units/unit.h>
+#include <mp-units/framework.h>
 #endif
+// IWYU pragma: end_exports
 
 MP_UNITS_EXPORT
 namespace mp_units::typographic {
diff --git a/src/systems/include/mp-units/systems/usc/usc.h b/src/systems/include/mp-units/systems/usc/usc.h
index 7a1971fd..d8da48f2 100644
--- a/src/systems/include/mp-units/systems/usc/usc.h
+++ b/src/systems/include/mp-units/systems/usc/usc.h
@@ -23,11 +23,14 @@
 #pragma once
 
 #include <mp-units/bits/module_macros.h>
+
+// IWYU pragma: begin_exports
 #include <mp-units/systems/international/international.h>
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
-#include <mp-units/unit.h>
+#include <mp-units/framework.h>
 #endif
+// IWYU pragma: end_exports
 
 MP_UNITS_EXPORT
 namespace mp_units::usc {
diff --git a/test/runtime/almost_equals.h b/test/runtime/almost_equals.h
index 471f2b79..9a6f3bfd 100644
--- a/test/runtime/almost_equals.h
+++ b/test/runtime/almost_equals.h
@@ -27,7 +27,7 @@
 import mp_units;
 #else
 #include <mp-units/format.h>
-#include <mp-units/quantity.h>
+#include <mp-units/framework/quantity.h>
 #endif
 
 namespace mp_units {
diff --git a/test/runtime/atomic_test.cpp b/test/runtime/atomic_test.cpp
index ba382edf..182e55a4 100644
--- a/test/runtime/atomic_test.cpp
+++ b/test/runtime/atomic_test.cpp
@@ -20,11 +20,15 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
-#include <catch2/catch_all.hpp>
-#include <mp-units/systems/isq/space_and_time.h>
-#include <mp-units/systems/si/unit_symbols.h>
-#include <mp-units/systems/si/units.h>
+#include <catch2/catch_test_macros.hpp>
 #include <atomic>
+#ifdef MP_UNITS_MODULES
+import mp_units;
+#else
+#include <mp-units/ostream.h>  // IWYU pragma: keep
+#include <mp-units/systems/isq/space_and_time.h>
+#include <mp-units/systems/si/si.h>
+#endif
 
 using namespace mp_units;
 using namespace mp_units::si::unit_symbols;
diff --git a/test/runtime/distribution_test.cpp b/test/runtime/distribution_test.cpp
index d3786989..faa84271 100644
--- a/test/runtime/distribution_test.cpp
+++ b/test/runtime/distribution_test.cpp
@@ -22,16 +22,18 @@
 
 #include <catch2/catch_test_macros.hpp>
 #include <array>
+#include <cstddef>
+#include <cstdint>
 #include <initializer_list>
 #include <random>
 #include <vector>
 #ifdef MP_UNITS_MODULES
 import mp_units;
 #else
-#include <mp-units/ostream.h>
+#include <mp-units/ostream.h>  // IWYU pragma: keep
 #include <mp-units/random.h>
-#include <mp-units/systems/si/unit_symbols.h>
-#include <mp-units/systems/si/units.h>
+#include <mp-units/systems/isq/space_and_time.h>
+#include <mp-units/systems/si/si.h>
 #endif
 
 
diff --git a/test/runtime/fmt_test.cpp b/test/runtime/fmt_test.cpp
index d1a27028..54c9221d 100644
--- a/test/runtime/fmt_test.cpp
+++ b/test/runtime/fmt_test.cpp
@@ -30,9 +30,9 @@
 #ifdef MP_UNITS_MODULES
 import mp_units;
 #else
-#include <mp-units/customization_points.h>
 #include <mp-units/format.h>
-#include <mp-units/ostream.h>
+#include <mp-units/framework/customization_points.h>
+#include <mp-units/ostream.h>  // IWYU pragma: keep
 #include <mp-units/systems/cgs/cgs.h>
 #include <mp-units/systems/isq/electromagnetism.h>
 #include <mp-units/systems/isq/mechanics.h>
diff --git a/test/runtime/linear_algebra_test.cpp b/test/runtime/linear_algebra_test.cpp
index 5779fbb9..bbf584db 100644
--- a/test/runtime/linear_algebra_test.cpp
+++ b/test/runtime/linear_algebra_test.cpp
@@ -22,15 +22,14 @@
 
 #include <catch2/catch_test_macros.hpp>
 #include <mp-units/compat_macros.h>
-#include <cmath>
 #include <matrix>
+#include <ostream>
 #ifdef MP_UNITS_MODULES
 import mp_units;
 #else
-#include <mp-units/customization_points.h>
 #include <mp-units/format.h>
 #include <mp-units/math.h>
-#include <mp-units/ostream.h>
+#include <mp-units/ostream.h>  // IWYU pragma: keep
 #include <mp-units/systems/isq/mechanics.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/si/si.h>
diff --git a/test/runtime/math_test.cpp b/test/runtime/math_test.cpp
index 7eab3fb1..578058e3 100644
--- a/test/runtime/math_test.cpp
+++ b/test/runtime/math_test.cpp
@@ -21,13 +21,14 @@
 // SOFTWARE.
 
 #include "almost_equals.h"
-#include <catch2/catch_all.hpp>
+#include <catch2/catch_test_macros.hpp>
+#include <catch2/matchers/catch_matchers.hpp>
 #include <limits>
 #ifdef MP_UNITS_MODULES
 import mp_units;
 #else
 #include <mp-units/math.h>
-#include <mp-units/ostream.h>
+#include <mp-units/ostream.h>  // IWYU pragma: keep
 #include <mp-units/systems/angular/angular.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/si/si.h>
diff --git a/test/static/cgs_test.cpp b/test/static/cgs_test.cpp
index c58c5885..bcd927af 100644
--- a/test/static/cgs_test.cpp
+++ b/test/static/cgs_test.cpp
@@ -24,7 +24,7 @@
 #include <mp-units/systems/cgs/cgs.h>
 #include <mp-units/systems/isq/mechanics.h>
 #include <mp-units/systems/isq/space_and_time.h>
-#include <mp-units/systems/si/unit_symbols.h>
+#include <mp-units/systems/si/units.h>
 
 template<class T>
   requires mp_units::is_scalar<T>
diff --git a/test/static/chrono_test.cpp b/test/static/chrono_test.cpp
index ba881fa1..12319ea2 100644
--- a/test/static/chrono_test.cpp
+++ b/test/static/chrono_test.cpp
@@ -21,9 +21,12 @@
 // SOFTWARE.
 
 #include "test_tools.h"
-#include <mp-units/bits/external/type_traits.h>
-#include <mp-units/quantity_point.h>
+#include <mp-units/ext/type_traits.h>
+#include <mp-units/framework/quantity_point.h>  // IWYU pragma: keep
+#include <mp-units/systems/isq/si_quantities.h>
 #include <mp-units/systems/si/si.h>
+#include <chrono>
+#include <concepts>
 #include <ratio>
 
 namespace {
diff --git a/test/static/compare_test.cpp b/test/static/compare_test.cpp
index 5de812d9..422dd569 100644
--- a/test/static/compare_test.cpp
+++ b/test/static/compare_test.cpp
@@ -20,7 +20,7 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
-#include <mp-units/compare.h>
+#include <mp-units/framework/compare.h>  // IWYU pragma: keep
 #include <mp-units/systems/si/si.h>
 
 namespace {
diff --git a/test/static/concepts_test.cpp b/test/static/concepts_test.cpp
index e97a1df7..38d598f3 100644
--- a/test/static/concepts_test.cpp
+++ b/test/static/concepts_test.cpp
@@ -20,8 +20,6 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
-#include <mp-units/concepts.h>
-#include <mp-units/quantity_point.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/natural/natural.h>
 #include <mp-units/systems/si/si.h>
@@ -29,6 +27,7 @@
 #include <complex>
 #include <optional>
 #include <string>
+#include <type_traits>
 
 template<typename T>
 inline constexpr bool mp_units::is_scalar<std::complex<T>> = true;
diff --git a/test/static/custom_rep_test_min_impl.cpp b/test/static/custom_rep_test_min_impl.cpp
index ef3ba8db..75e63330 100644
--- a/test/static/custom_rep_test_min_impl.cpp
+++ b/test/static/custom_rep_test_min_impl.cpp
@@ -20,7 +20,9 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
-#include <mp-units/bits/external/hacks.h>
+#include <mp-units/bits/hacks.h>
+#include <mp-units/framework.h>
+#include <mp-units/systems/si/prefixes.h>
 #include <mp-units/systems/si/units.h>
 #include <concepts>
 #include <type_traits>
diff --git a/test/static/dimension_symbol_test.cpp b/test/static/dimension_symbol_test.cpp
index 048ac692..f1ce708e 100644
--- a/test/static/dimension_symbol_test.cpp
+++ b/test/static/dimension_symbol_test.cpp
@@ -20,7 +20,9 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
+#include <mp-units/framework.h>
 #include <mp-units/systems/isq/isq.h>
+#include <string_view>
 
 namespace {
 
diff --git a/test/static/dimension_test.cpp b/test/static/dimension_test.cpp
index 808620d7..33f80262 100644
--- a/test/static/dimension_test.cpp
+++ b/test/static/dimension_test.cpp
@@ -21,11 +21,9 @@
 // SOFTWARE.
 
 #include "test_tools.h"
-#include <mp-units/dimension.h>
-#include <mp-units/quantity.h>
-#include <mp-units/quantity_spec.h>
-#include <mp-units/reference.h>
-#include <mp-units/unit.h>
+#include <mp-units/ext/type_traits.h>
+#include <mp-units/framework.h>
+#include <type_traits>
 
 namespace {
 
diff --git a/test/static/fixed_string_test.cpp b/test/static/fixed_string_test.cpp
index 97f1c15f..93890a98 100644
--- a/test/static/fixed_string_test.cpp
+++ b/test/static/fixed_string_test.cpp
@@ -20,7 +20,8 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
-#include <mp-units/bits/external/fixed_string.h>
+#include <mp-units/ext/fixed_string.h>
+#include <string_view>
 
 using namespace mp_units;
 
diff --git a/test/static/fractional_exponent_quantity.cpp b/test/static/fractional_exponent_quantity.cpp
index ce82795d..aca6f206 100644
--- a/test/static/fractional_exponent_quantity.cpp
+++ b/test/static/fractional_exponent_quantity.cpp
@@ -21,8 +21,10 @@
 // SOFTWARE.
 
 #include <mp-units/compat_macros.h>
+#include <mp-units/framework.h>
 #include <mp-units/math.h>
 #include <mp-units/systems/isq/electromagnetism.h>
+#include <mp-units/systems/isq/si_quantities.h>
 #include <mp-units/systems/si/units.h>
 
 namespace {
diff --git a/test/static/hep_test.cpp b/test/static/hep_test.cpp
index 93a95321..82e2a07d 100644
--- a/test/static/hep_test.cpp
+++ b/test/static/hep_test.cpp
@@ -22,7 +22,6 @@
 
 #include <mp-units/systems/hep/hep.h>
 #include <mp-units/systems/isq/mechanics.h>
-#include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/si/si.h>
 
 template<class T>
diff --git a/test/static/iau_test.cpp b/test/static/iau_test.cpp
index d05fc28e..ca298e98 100644
--- a/test/static/iau_test.cpp
+++ b/test/static/iau_test.cpp
@@ -20,7 +20,7 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
-#include <mp-units/math.h>
+#include <mp-units/math.h>  // IWYU pragma: keep
 #include <mp-units/systems/iau/iau.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/si/si.h>
diff --git a/test/static/iec80000_test.cpp b/test/static/iec80000_test.cpp
index 2718758f..2b3b3828 100644
--- a/test/static/iec80000_test.cpp
+++ b/test/static/iec80000_test.cpp
@@ -20,10 +20,9 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
-#include <mp-units/quantity.h>
-#include <mp-units/reference.h>
 #include <mp-units/systems/iec80000/iec80000.h>
-#include <mp-units/systems/si/unit_symbols.h>
+#include <mp-units/systems/isq/base_quantities.h>
+#include <mp-units/systems/si/si.h>
 
 /* ************** DERIVED DIMENSIONS THAT INCLUDE UNITS WITH SPECIAL NAMES **************** */
 
diff --git a/test/static/imperial_test.cpp b/test/static/imperial_test.cpp
index 7b3b3a74..8809ca19 100644
--- a/test/static/imperial_test.cpp
+++ b/test/static/imperial_test.cpp
@@ -22,7 +22,6 @@
 
 #include <mp-units/systems/imperial/imperial.h>
 #include <mp-units/systems/isq/space_and_time.h>
-#include <mp-units/systems/si/unit_symbols.h>
 
 namespace {
 
diff --git a/test/static/isq_angle_test.cpp b/test/static/isq_angle_test.cpp
index ef597076..09d0b9ee 100644
--- a/test/static/isq_angle_test.cpp
+++ b/test/static/isq_angle_test.cpp
@@ -21,7 +21,7 @@
 // SOFTWARE.
 
 #include <mp-units/systems/isq_angle/isq_angle.h>
-#include <mp-units/systems/si/unit_symbols.h>
+#include <mp-units/systems/si/si.h>
 
 namespace {
 
diff --git a/test/static/isq_test.cpp b/test/static/isq_test.cpp
index 41cd4ec5..1cba2803 100644
--- a/test/static/isq_test.cpp
+++ b/test/static/isq_test.cpp
@@ -20,9 +20,9 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
-#include <mp-units/reference.h>
+#include <mp-units/framework.h>
 #include <mp-units/systems/isq/isq.h>
-#include <mp-units/systems/si/unit_symbols.h>
+#include <mp-units/systems/si/si.h>
 
 namespace {
 
diff --git a/test/static/math_test.cpp b/test/static/math_test.cpp
index 68c87848..d27c4c02 100644
--- a/test/static/math_test.cpp
+++ b/test/static/math_test.cpp
@@ -22,9 +22,7 @@
 
 #include <mp-units/math.h>  // IWYU pragma: keep
 #include <mp-units/systems/international/international.h>
-#include <mp-units/systems/isq/space_and_time.h>
-#include <mp-units/systems/si/unit_symbols.h>
-#include <optional>
+#include <mp-units/systems/si/si.h>
 
 namespace {
 
diff --git a/test/static/natural_test.cpp b/test/static/natural_test.cpp
index 7880642b..06a2b597 100644
--- a/test/static/natural_test.cpp
+++ b/test/static/natural_test.cpp
@@ -21,6 +21,8 @@
 // SOFTWARE.
 
 #include <mp-units/math.h>
+#include <mp-units/systems/isq/mechanics.h>
+#include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/natural/natural.h>
 
 template<class T>
diff --git a/test/static/prime_test.cpp b/test/static/prime_test.cpp
index 0fd724bd..21a7b571 100644
--- a/test/static/prime_test.cpp
+++ b/test/static/prime_test.cpp
@@ -20,8 +20,9 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
-#include <mp-units/bits/external/prime.h>
-#include <type_traits>
+#include <mp-units/ext/prime.h>
+#include <array>
+#include <cstddef>
 #include <utility>
 
 using namespace mp_units::detail;
diff --git a/test/static/quantity_point_test.cpp b/test/static/quantity_point_test.cpp
index f9d4e314..01e3a271 100644
--- a/test/static/quantity_point_test.cpp
+++ b/test/static/quantity_point_test.cpp
@@ -21,10 +21,13 @@
 // SOFTWARE.
 
 #include "test_tools.h"
-#include <mp-units/quantity_point.h>
+#include <mp-units/compat_macros.h>
+#include <mp-units/ext/type_traits.h>
 #include <mp-units/systems/isq/isq.h>
 #include <mp-units/systems/si/si.h>
 #include <mp-units/systems/usc/usc.h>
+#include <chrono>
+#include <concepts>
 #include <cstdint>
 #include <limits>
 #include <type_traits>
diff --git a/test/static/quantity_spec_test.cpp b/test/static/quantity_spec_test.cpp
index 46c233fa..49a2d87a 100644
--- a/test/static/quantity_spec_test.cpp
+++ b/test/static/quantity_spec_test.cpp
@@ -21,10 +21,9 @@
 // SOFTWARE.
 
 #include "test_tools.h"
-#include <mp-units/quantity.h>
-#include <mp-units/quantity_spec.h>
-#include <mp-units/reference.h>
-#include <mp-units/unit.h>
+#include <mp-units/ext/type_traits.h>
+#include <mp-units/framework.h>
+#include <type_traits>
 
 namespace {
 
diff --git a/test/static/quantity_test.cpp b/test/static/quantity_test.cpp
index 5635622b..5dfacbb2 100644
--- a/test/static/quantity_test.cpp
+++ b/test/static/quantity_test.cpp
@@ -21,12 +21,17 @@
 // SOFTWARE.
 
 #include "test_tools.h"
-#include <mp-units/bits/external/hacks.h>
+#include <mp-units/bits/hacks.h>
+#include <mp-units/ext/fixed_string.h>
+#include <mp-units/ext/type_traits.h>
 #include <mp-units/systems/isq/mechanics.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/si/si.h>
+#include <chrono>
+#include <concepts>
 #include <cstdint>
 #include <limits>
+#include <type_traits>
 #include <utility>
 
 template<>
diff --git a/test/static/reference_test.cpp b/test/static/reference_test.cpp
index a1045ce3..4c4803a7 100644
--- a/test/static/reference_test.cpp
+++ b/test/static/reference_test.cpp
@@ -21,13 +21,10 @@
 // SOFTWARE.
 
 #include "test_tools.h"
-#include <mp-units/dimension.h>
-#include <mp-units/quantity.h>
-#include <mp-units/quantity_spec.h>
-#include <mp-units/reference.h>
-#include <mp-units/system_reference.h>
+#include <mp-units/framework.h>
 #include <mp-units/systems/si/prefixes.h>
-#include <mp-units/unit.h>
+#include <cstdint>
+#include <type_traits>
 
 namespace {
 
diff --git a/test/static/symbol_text_test.cpp b/test/static/symbol_text_test.cpp
index f11d0789..10de7f92 100644
--- a/test/static/symbol_text_test.cpp
+++ b/test/static/symbol_text_test.cpp
@@ -20,7 +20,8 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
-#include <mp-units/bits/symbol_text.h>
+#include <mp-units/ext/fixed_string.h>
+#include <mp-units/framework.h>
 
 using namespace mp_units;
 
diff --git a/test/static/test_tools.h b/test/static/test_tools.h
index 2c9bf801..73f79613 100644
--- a/test/static/test_tools.h
+++ b/test/static/test_tools.h
@@ -22,8 +22,8 @@
 
 #pragma once
 
-#include <mp-units/bits/external/hacks.h>
-#include <mp-units/quantity_spec.h>
+#include <mp-units/bits/hacks.h>
+#include <mp-units/framework/quantity_spec.h>
 #include <type_traits>
 
 template<auto V, typename T>
diff --git a/test/static/type_list_test.cpp b/test/static/type_list_test.cpp
index 1c994f35..6733a231 100644
--- a/test/static/type_list_test.cpp
+++ b/test/static/type_list_test.cpp
@@ -20,8 +20,8 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
-#include <mp-units/bits/external/type_list.h>
-#include <mp-units/bits/external/type_traits.h>
+#include <mp-units/bits/type_list.h>
+#include <mp-units/ext/type_traits.h>
 #include <type_traits>
 
 namespace {
diff --git a/test/static/unit_symbol_test.cpp b/test/static/unit_symbol_test.cpp
index fcbebbdb..cec62112 100644
--- a/test/static/unit_symbol_test.cpp
+++ b/test/static/unit_symbol_test.cpp
@@ -23,6 +23,7 @@
 #include <mp-units/systems/iau/iau.h>
 #include <mp-units/systems/iec80000/iec80000.h>
 #include <mp-units/systems/si/si.h>
+#include <string_view>
 
 namespace {
 
diff --git a/test/static/unit_test.cpp b/test/static/unit_test.cpp
index 590a147f..2d4a6092 100644
--- a/test/static/unit_test.cpp
+++ b/test/static/unit_test.cpp
@@ -21,11 +21,10 @@
 // SOFTWARE.
 
 #include "test_tools.h"
-#include <mp-units/dimension.h>
-#include <mp-units/quantity.h>
-#include <mp-units/reference.h>
+#include <mp-units/ext/type_traits.h>
+#include <mp-units/framework.h>
 #include <mp-units/systems/si/prefixes.h>
-#include <mp-units/unit.h>
+#include <type_traits>
 
 namespace {
 
@@ -336,11 +335,11 @@ static_assert(is_of_type<speed_of_light_in_vacuum * gram * standard_gravity,
 static_assert(is_of_type<gram * standard_gravity * speed_of_light_in_vacuum,
                          derived_unit<speed_of_light_in_vacuum_, gram_, standard_gravity_>>);
 
-static_assert(std::is_same_v<decltype(inverse(second) * metre), decltype(metre / second)>);
-static_assert(std::is_same_v<decltype(metre * inverse(second)), decltype(metre / second)>);
-static_assert(std::is_same_v<decltype((metre / second) * inverse(second)), decltype(metre / second / second)>);
-static_assert(std::is_same_v<decltype((metre / second) * inverse(second)), decltype(metre / (second * second))>);
-static_assert(std::is_same_v<decltype((metre / second) * inverse(second)), decltype(metre / square(second))>);
+static_assert(is_same_v<decltype(inverse(second) * metre), decltype(metre / second)>);
+static_assert(is_same_v<decltype(metre * inverse(second)), decltype(metre / second)>);
+static_assert(is_same_v<decltype((metre / second) * inverse(second)), decltype(metre / second / second)>);
+static_assert(is_same_v<decltype((metre / second) * inverse(second)), decltype(metre / (second * second))>);
+static_assert(is_same_v<decltype((metre / second) * inverse(second)), decltype(metre / square(second))>);
 
 
 // derived unit normalization
diff --git a/test/static/usc_test.cpp b/test/static/usc_test.cpp
index 45248d24..3f05ec49 100644
--- a/test/static/usc_test.cpp
+++ b/test/static/usc_test.cpp
@@ -20,10 +20,11 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
-#include <mp-units/bits/external/hacks.h>
+#include <mp-units/bits/hacks.h>
 #include <mp-units/systems/isq/mechanics.h>
 #include <mp-units/systems/isq/space_and_time.h>
-#include <mp-units/systems/si/unit_symbols.h>
+#include <mp-units/systems/si/prefixes.h>
+#include <mp-units/systems/si/units.h>
 #include <mp-units/systems/usc/usc.h>
 
 namespace {