Say C++17 everywhere the project describes itselfchore/cpp17-descriptions

The move to C++17 left a trail of older claims. The Runner's own
.clang-format still said c++20; the result is byte for byte the same under
either value. Premake and Xmake still compiled the library as C++20 and
the main library as C++14, which meant their CI jobs were not testing the
language the project promises. Both now use C++17 for every target.

The rest is text: the Meson pkg-config description claimed C++14, comments
in the CMake and Meson files explained requirements that no longer exist,
.clang-tidy gave C++14 as the reason for two exclusions, issue templates
asked for C++20 samples, and the example headers named -std=c++14 and
catch2-with-main. The release notes and the migration guide state the
C++17 minimum. Doxygen's brief called the project "Catch2's test API",
which presents it as Catch2. Meson declared only BSL-1.0; it now names both
licenses of the tree. The amalgamated files are regenerated.

27 files changed, 40 insertions, 50 deletions

diff --git a/.clang-tidy b/.clang-tidy
index 8d3a17f2..57acd162 100644
--- a/.clang-tidy
+++ b/.clang-tidy
@@ -28,11 +28,11 @@ Checks: >-
   -modernize-concat-nested-namespaces,
   -modernize-use-nodiscard,
   -modernize-use-default-member-init,
-  -modernize-type-traits,# we need to support C++14,
+  -modernize-type-traits,# the engine spells these out,
   -modernize-deprecated-headers,
   ,# There's a lot of these and most of them are probably not useful,
   -modernize-pass-by-value,
-  -modernize-use-string-view, # We support C++14,
+  -modernize-use-string-view, # the engine has its own StringRef,
 
   performance-*,
   performance-enum-size,
diff --git a/.github/ISSUE_TEMPLATE/bug_report.md b/.github/ISSUE_TEMPLATE/bug_report.md
index 7d640168..81c651c9 100644
--- a/.github/ISSUE_TEMPLATE/bug_report.md
+++ b/.github/ISSUE_TEMPLATE/bug_report.md
@@ -26,7 +26,7 @@ Describe the expected behavior and the contract or documentation that supports i
 
 ### Minimal reproduction
 
-Provide a small C++20 test, the command used to build and run it, and the test-runner arguments. For a property failure, include the root seed, replay seed, trial number, and minimized counterexample when available. For a snapshot failure, describe the snapshot mode and file location without pasting private content.
+Provide a small C++17 test, the command used to build and run it, and the test-runner arguments. For a property failure, include the root seed, replay seed, trial number, and minimized counterexample when available. For a snapshot failure, describe the snapshot mode and file location without pasting private content.
 
 ### Environment
 
diff --git a/.github/ISSUE_TEMPLATE/feature_request.md b/.github/ISSUE_TEMPLATE/feature_request.md
index 180a12dd..dd1ca2b2 100644
--- a/.github/ISSUE_TEMPLATE/feature_request.md
+++ b/.github/ISSUE_TEMPLATE/feature_request.md
@@ -15,7 +15,7 @@ What testing task is difficult today? Include a concrete example from a real tes
 
 ### Proposed behavior
 
-Describe the user-facing API or runner behavior, with a short C++20 example if useful. Explain how failures should be reported and reproduced.
+Describe the user-facing API or runner behavior, with a short C++17 example if useful. Explain how failures should be reported and reproduced.
 
 ### Ownership and compatibility
 
diff --git a/Doxyfile b/Doxyfile
index 0ee44da5..12d4bb3c 100644
--- a/Doxyfile
+++ b/Doxyfile
@@ -54,7 +54,7 @@ PROJECT_NUMBER         =
 # for a project that appears at the top of each page and should give viewer a
 # quick idea about the purpose of the project. Keep the description short.
 
-PROJECT_BRIEF          = "Catch2's test API with a parallel runner, property testing and snapshots"
+PROJECT_BRIEF          = "A C++ test framework with a parallel runner, property testing and snapshots"
 
 # With the PROJECT_LOGO tag one can specify a logo or an icon that is included
 # in the documentation. The maximum height of the logo should not exceed 55
diff --git a/docs/migrate-v2-to-v3.md b/docs/migrate-v2-to-v3.md
index bd030523..9ec1f1c7 100644
--- a/docs/migrate-v2-to-v3.md
+++ b/docs/migrate-v2-to-v3.md
@@ -7,7 +7,7 @@
 v3 is the next major version of Catch2 and brings three significant changes:
  * Catch2 is now split into multiple headers
  * Catch2 is now compiled as a static library
- * C++14 is the minimum required C++ version
+ * C++17 is the minimum required C++ version
 
 There are many reasons why we decided to go from the old single-header
 distribution model to a more standard library distribution model. The
diff --git a/docs/release-notes.md b/docs/release-notes.md
index 870541d4..0e3633de 100644
--- a/docs/release-notes.md
+++ b/docs/release-notes.md
@@ -71,8 +71,7 @@ line and reporters with [a runner of its own](progmasoft-runner.md#top):
 * Catch2's command line, reporters, `CATCH_REGISTER_REPORTER` and listing
   were removed; see [the command line](command-line.md#top) and
   [reports](reporters.md#top). Listeners keep working.
-* The library is compiled as C++20; code that includes only the engine's
-  headers still needs C++14.
+* C++17 is the minimum, for the library and for the code that uses it.
 * The results model in `Progmasoft/Catch3/Results.hpp` was rewritten around
   tests and attempts.
 * Conan packaging was dropped.
diff --git a/examples/010-TestCase.cpp b/examples/010-TestCase.cpp
index 5eb982c8..d4c42a48 100644
--- a/examples/010-TestCase.cpp
+++ b/examples/010-TestCase.cpp
@@ -27,7 +27,7 @@ TEST_CASE( "Factorials of 1 and higher are computed (pass)", "[single-file]" ) {
 }
 
 // Compile & run:
-// - g++ -std=c++14 -Wall -I$(CATCH_SINGLE_INCLUDE) -o 010-TestCase 010-TestCase.cpp && 010-TestCase --success
+// - g++ -std=c++17 -Wall -I$(CATCH_SINGLE_INCLUDE) -o 010-TestCase 010-TestCase.cpp && 010-TestCase --success
 // - cl -EHsc -I%CATCH_SINGLE_INCLUDE% 010-TestCase.cpp && 010-TestCase --success
 
 // Expected compact output (all assertions):
diff --git a/examples/020-TestCase-1.cpp b/examples/020-TestCase-1.cpp
index 86de07a9..1acdc7a0 100644
--- a/examples/020-TestCase-1.cpp
+++ b/examples/020-TestCase-1.cpp
@@ -18,8 +18,8 @@ TEST_CASE( "1: All test cases reside in other .cpp files (empty)", "[multi-file:
 // Here just to show there are two source files via option --list-tests.
 
 // Compile & run:
-// - g++ -std=c++14 -Wall -I$(CATCH_SINGLE_INCLUDE) -c 020-TestCase-1.cpp
-// - g++ -std=c++14 -Wall -I$(CATCH_SINGLE_INCLUDE) -o 020-TestCase TestCase-1.o 020-TestCase-2.cpp && 020-TestCase --success
+// - g++ -std=c++17 -Wall -I$(CATCH_SINGLE_INCLUDE) -c 020-TestCase-1.cpp
+// - g++ -std=c++17 -Wall -I$(CATCH_SINGLE_INCLUDE) -o 020-TestCase TestCase-1.o 020-TestCase-2.cpp && 020-TestCase --success
 //
 // - cl -EHsc -I%CATCH_SINGLE_INCLUDE% -c 020-TestCase-1.cpp
 // - cl -EHsc -I%CATCH_SINGLE_INCLUDE% -Fe020-TestCase.exe 020-TestCase-1.obj 020-TestCase-2.cpp && 020-TestCase --success
diff --git a/examples/030-Asn-Require-Check.cpp b/examples/030-Asn-Require-Check.cpp
index ed6ad752..416db4bc 100644
--- a/examples/030-Asn-Require-Check.cpp
+++ b/examples/030-Asn-Require-Check.cpp
@@ -61,7 +61,7 @@ TEST_CASE( "Assert that something is false (continue after failure)", "[check-fa
 }
 
 // Compile & run:
-// - g++ -std=c++14 -Wall -I$(CATCH_SINGLE_INCLUDE) -o 030-Asn-Require-Check 030-Asn-Require-Check.cpp && 030-Asn-Require-Check --success
+// - g++ -std=c++17 -Wall -I$(CATCH_SINGLE_INCLUDE) -o 030-Asn-Require-Check 030-Asn-Require-Check.cpp && 030-Asn-Require-Check --success
 // - cl -EHsc -I%CATCH_SINGLE_INCLUDE% 030-Asn-Require-Check.cpp && 030-Asn-Require-Check --success
 
 // Expected compact output (all assertions):
diff --git a/examples/100-Fix-Section.cpp b/examples/100-Fix-Section.cpp
index d1e4cdbc..b095d78b 100644
--- a/examples/100-Fix-Section.cpp
+++ b/examples/100-Fix-Section.cpp
@@ -53,7 +53,7 @@ TEST_CASE( "vectors can be sized and resized", "[vector]" ) {
 }
 
 // Compile & run:
-// - g++ -std=c++14 -Wall -I$(CATCH_SINGLE_INCLUDE) -o 100-Fix-Section 100-Fix-Section.cpp && 100-Fix-Section --success
+// - g++ -std=c++17 -Wall -I$(CATCH_SINGLE_INCLUDE) -o 100-Fix-Section 100-Fix-Section.cpp && 100-Fix-Section --success
 // - cl -EHsc -I%CATCH_SINGLE_INCLUDE% 100-Fix-Section.cpp && 100-Fix-Section --success
 
 // Expected compact output (all assertions):
diff --git a/examples/110-Fix-ClassFixture.cpp b/examples/110-Fix-ClassFixture.cpp
index 1b3f053f..f988f676 100644
--- a/examples/110-Fix-ClassFixture.cpp
+++ b/examples/110-Fix-ClassFixture.cpp
@@ -60,11 +60,11 @@ TEST_CASE_METHOD( UniqueTestsFixture, "Create Employee/Normal", "[create]" ) {
 }
 
 // Compile & run:
-// - g++ -std=c++14 -Wall -I$(CATCH_SINGLE_INCLUDE) -o 110-Fix-ClassFixture 110-Fix-ClassFixture.cpp && 110-Fix-ClassFixture --success
+// - g++ -std=c++17 -Wall -I$(CATCH_SINGLE_INCLUDE) -o 110-Fix-ClassFixture 110-Fix-ClassFixture.cpp && 110-Fix-ClassFixture --success
 // - cl -EHsc -I%CATCH_SINGLE_INCLUDE% 110-Fix-ClassFixture.cpp && 110-Fix-ClassFixture --success
 //
 // Compile with pkg-config:
-// - g++ -std=c++14 -Wall $(pkg-config catch2-with-main --cflags)  -o 110-Fix-ClassFixture 110-Fix-ClassFixture.cpp $(pkg-config catch2-with-main --libs)
+// - g++ -std=c++17 -Wall $(pkg-config catch3-with-main --cflags)  -o 110-Fix-ClassFixture 110-Fix-ClassFixture.cpp $(pkg-config catch3-with-main --libs)
 
 // Expected compact output (all assertions):
 //
diff --git a/examples/120-Bdd-ScenarioGivenWhenThen.cpp b/examples/120-Bdd-ScenarioGivenWhenThen.cpp
index b3edcd8c..1446393c 100644
--- a/examples/120-Bdd-ScenarioGivenWhenThen.cpp
+++ b/examples/120-Bdd-ScenarioGivenWhenThen.cpp
@@ -56,7 +56,7 @@ SCENARIO( "vectors can be sized and resized", "[vector]" ) {
 }
 
 // Compile & run:
-// - g++ -std=c++14 -Wall -I$(CATCH_SINGLE_INCLUDE) -o 120-Bdd-ScenarioGivenWhenThen 120-Bdd-ScenarioGivenWhenThen.cpp && 120-Bdd-ScenarioGivenWhenThen --success
+// - g++ -std=c++17 -Wall -I$(CATCH_SINGLE_INCLUDE) -o 120-Bdd-ScenarioGivenWhenThen 120-Bdd-ScenarioGivenWhenThen.cpp && 120-Bdd-ScenarioGivenWhenThen --success
 // - cl -EHsc -I%CATCH_SINGLE_INCLUDE% 120-Bdd-ScenarioGivenWhenThen.cpp && 120-Bdd-ScenarioGivenWhenThen --success
 
 // Expected compact output (all assertions):
diff --git a/examples/210-Evt-EventListeners.cpp b/examples/210-Evt-EventListeners.cpp
index 48ccce20..5c09d283 100644
--- a/examples/210-Evt-EventListeners.cpp
+++ b/examples/210-Evt-EventListeners.cpp
@@ -419,7 +419,7 @@ TEST_CASE_METHOD( Fixture, "3: Testcase with class-based fixture", "[tag-C][tag-
 }
 
 // Compile & run:
-// - g++ -std=c++14 -Wall -I$(CATCH_SINGLE_INCLUDE) -o 210-Evt-EventListeners 210-Evt-EventListeners.cpp && 210-Evt-EventListeners --success
+// - g++ -std=c++17 -Wall -I$(CATCH_SINGLE_INCLUDE) -o 210-Evt-EventListeners 210-Evt-EventListeners.cpp && 210-Evt-EventListeners --success
 // - cl -EHsc -I%CATCH_SINGLE_INCLUDE% 210-Evt-EventListeners.cpp && 210-Evt-EventListeners --success
 
 // Expected compact output (all assertions):
diff --git a/extras/catch_amalgamated.cpp b/extras/catch_amalgamated.cpp
index 3151faf3..7556181e 100644
--- a/extras/catch_amalgamated.cpp
+++ b/extras/catch_amalgamated.cpp
@@ -7,7 +7,7 @@
 // SPDX-License-Identifier: BSL-1.0
 
 //  Catch3 v0.3.0, on the Catch2 v3.16.1 engine
-//  Generated: 2026-10-31 20:20:20.891771
+//  Generated: 2026-11-01 00:25:29.768099
 //  ----------------------------------------------------------
 //  This file is an amalgamation of multiple different files.
 //  You probably shouldn't edit it directly.
diff --git a/extras/catch_amalgamated.hpp b/extras/catch_amalgamated.hpp
index f26b0811..513c91ae 100644
--- a/extras/catch_amalgamated.hpp
+++ b/extras/catch_amalgamated.hpp
@@ -7,7 +7,7 @@
 // SPDX-License-Identifier: BSL-1.0
 
 //  Catch3 v0.3.0, on the Catch2 v3.16.1 engine
-//  Generated: 2026-10-31 20:20:20.604513
+//  Generated: 2026-11-01 00:25:29.668428
 //  ----------------------------------------------------------
 //  This file is an amalgamation of multiple different files.
 //  You probably shouldn't edit it directly.
@@ -5942,7 +5942,7 @@ namespace Detail {
 namespace Catch {
 
     namespace Detail {
-        // This was added in C++20, but we require only C++14 for now.
+        // This was added in C++20, but we require only C++17.
         template <typename T>
         using RemoveCVRef_t = std::remove_cv_t<std::remove_reference_t<T>>;
     }
diff --git a/extras/catch_amalgamated_third_party.hpp b/extras/catch_amalgamated_third_party.hpp
index 6a48d4dd..353e0009 100644
--- a/extras/catch_amalgamated_third_party.hpp
+++ b/extras/catch_amalgamated_third_party.hpp
@@ -1,5 +1,5 @@
 // Catch3 v0.3.0: yyjson and pugixml for catch_amalgamated.cpp
-// Generated: 2026-10-31 20:20:21.165039
+// Generated: 2026-11-01 00:25:29.854771
 // ----------------------------------------------------------
 // This file is an amalgamation of src/Progmasoft/Runner/Yyjson.inl,
 // src/Progmasoft/PugiXml.inl and the libraries they include from
diff --git a/fuzzing/CMakeLists.txt b/fuzzing/CMakeLists.txt
index 03e205ce..436642c6 100644
--- a/fuzzing/CMakeLists.txt
+++ b/fuzzing/CMakeLists.txt
@@ -7,7 +7,7 @@
 add_library(fuzzhelper NullOStream.h NullOStream.cpp)
 target_link_libraries(fuzzhelper PUBLIC Catch3::Catch3)
 
-# The runner fuzzers include its C++20 headers.
+# The runner fuzzers include its headers, which need C++17.
 target_compile_features(fuzzhelper PUBLIC cxx_std_17)
 
 # This should be possible to set from the outside to be oss-fuzz compatible,
diff --git a/meson.build b/meson.build
index 4329a2f9..d63151e0 100644
--- a/meson.build
+++ b/meson.build
@@ -9,8 +9,8 @@ project(
   'catch3',
   'cpp',
   version: '0.3.0',
-  license: 'BSL-1.0',
-  # Meson 1.1 added clang-cl support for the C++20 mode used by Progmasoft tests.
+  license: ['BSL-1.0', 'MPL-2.0 WITH AdditionRef-Progmasoft-Exception-2.0'],
+  # Meson 1.1 added clang-cl support for the C++ modes used by Progmasoft tests.
   meson_version: '>=1.1.0',
 )
 
diff --git a/premake5.lua b/premake5.lua
index d8a005d5..a1427cf3 100644
--- a/premake5.lua
+++ b/premake5.lua
@@ -33,12 +33,11 @@ workspace "Catch3"
     filter {}
 
 -- The Catch2-compatible engine, the Catch3 runner, property testing and
--- snapshots; the library is C++20, the engine's headers need only C++14 in
--- the code that includes them.
+-- snapshots; the library and the code that includes it need C++17.
 project "Catch3"
     kind "StaticLib"
     language "C++"
-    cppdialect "C++20"
+    cppdialect "C++17"
     targetdir "build/premake/bin/%{cfg.buildcfg}"
     objdir "build/premake/obj/Catch3/%{cfg.buildcfg}"
     files {
@@ -64,7 +63,7 @@ project "Catch3"
 project "Catch3WithMain"
     kind "StaticLib"
     language "C++"
-    cppdialect "C++14"
+    cppdialect "C++17"
     -- Visual Studio injects UNICODE for Windows projects, which would select
     -- Catch2's wmain entry point instead of the normal console main.
     defines { "DO_NOT_USE_WMAIN" }
@@ -77,7 +76,7 @@ project "Catch3WithMain"
 project "ProgmasoftPropertyTests"
     kind "ConsoleApp"
     language "C++"
-    cppdialect "C++20"
+    cppdialect "C++17"
     targetdir "build/premake/bin/%{cfg.buildcfg}"
     objdir "build/premake/obj/ProgmasoftPropertyTests/%{cfg.buildcfg}"
     files {
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 398260fd..aee8c7a3 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -396,8 +396,7 @@ set_target_properties(Catch3 PROPERTIES
   SOVERSION ${PROJECT_VERSION}
 )
 
-# Code that includes the engine's headers needs C++14, and the other
-# Progmasoft/ headers C++20; the library itself, with the runner, is built as C++20.
+# The library, and the code that includes its headers, need C++17.
 target_compile_features(Catch3 PUBLIC cxx_std_17)
 
 configure_file(
@@ -489,7 +488,7 @@ if(CATCH3_BUILD_EXAMPLES OR CATCH3_BUILD_EXTRA_TESTS)
       Catch3Pugixml
   )
   # These targets compile the library's sources themselves, the runner's
-  # among them, which need C++20.
+  # among them, which need C++17.
   target_compile_features(Catch3_buildall_interface INTERFACE cxx_std_17)
 endif()
 
diff --git a/src/Progmasoft/Catch3/Internal/Decomposer.hpp b/src/Progmasoft/Catch3/Internal/Decomposer.hpp
index 77a4a123..4c57d3be 100644
--- a/src/Progmasoft/Catch3/Internal/Decomposer.hpp
+++ b/src/Progmasoft/Catch3/Internal/Decomposer.hpp
@@ -128,7 +128,7 @@
 namespace Catch {
 
     namespace Detail {
-        // This was added in C++20, but we require only C++14 for now.
+        // This was added in C++20, but we require only C++17.
         template <typename T>
         using RemoveCVRef_t = std::remove_cv_t<std::remove_reference_t<T>>;
     }
diff --git a/src/Progmasoft/Catch3/meson.build b/src/Progmasoft/Catch3/meson.build
index b8d38908..7b75dc6d 100644
--- a/src/Progmasoft/Catch3/meson.build
+++ b/src/Progmasoft/Catch3/meson.build
@@ -347,8 +347,7 @@ if ((host_machine.system() == 'android') or
   catch3_dependencies += log_dep
 endif
 
-# Code that includes the engine's headers needs C++14, and the other
-# Progmasoft/ headers C++20; the library itself, with the runner, is built as C++20.
+# The library, and the code that includes its headers, need C++17.
 catch3 = static_library(
   'Catch3',
   sources,
@@ -368,7 +367,7 @@ if get_option('install')
   pkg.generate(
     catch3,
     filebase: 'catch3',
-    description: 'A C++ test framework with a Catch2-compatible API; headers need C++14 and above',
+    description: 'A C++ test framework with a Catch2-compatible API; headers need C++17 and above',
     url: 'https://github.com/Progmasoft/catch3',
   )
 endif
diff --git a/src/Progmasoft/Runner/.clang-format b/src/Progmasoft/Runner/.clang-format
index 1063b9ea..2cdf8220 100644
--- a/src/Progmasoft/Runner/.clang-format
+++ b/src/Progmasoft/Runner/.clang-format
@@ -1,7 +1,7 @@
 ---
 Language: Cpp
 BasedOnStyle: LLVM
-Standard: c++20
+Standard: c++17
 
 UseTab: Never
 IndentWidth: 4
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index a5524a38..33bbc4b5 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -31,9 +31,8 @@ if(CATCH3_BUILD_SURROGATES)
   # Extracts all non-helper (e.g. Progmasoft/Catch3/All.hpp) headers from the
   # Catch3 target, and returns them through the argument.
   function(ExtractCatch3Headers OutArg)
-    # The engine's headers are the ones that come from Catch2. The other
-    # headers need C++20; the surrogates check the engine's headers at the
-    # language level of the build.
+    # The engine's headers are the ones that come from Catch2; the surrogates
+    # check them at the language level of the build.
     file(STRINGS "${CATCH_DIR}/tools/scripts/upstreamFiles.txt" upstreamFiles REGEX "^src/")
     get_target_property(targetSources Catch3 SOURCES)
     foreach(Source ${targetSources})
@@ -153,8 +152,7 @@ add_executable(SelfTest ${TEST_SOURCES} ${TEST_HEADERS})
 target_include_directories(SelfTest PRIVATE ${SELF_TEST_DIR})
 target_link_libraries(SelfTest PRIVATE Catch3WithMain)
 
-# Exercise the C++20 Progmasoft layer independently so the upstream Catch2
-# SelfTest continues to compile at its supported baseline language level.
+# Exercise the Progmasoft layer independently of the upstream Catch2 SelfTest.
 add_executable(ProgmasoftSelfTest
   Progmasoft/Generators.tests.cpp
   Progmasoft/Property.tests.cpp
diff --git a/tests/ExtraTests/CMakeLists.txt b/tests/ExtraTests/CMakeLists.txt
index e6488650..232b86dc 100644
--- a/tests/ExtraTests/CMakeLists.txt
+++ b/tests/ExtraTests/CMakeLists.txt
@@ -430,7 +430,7 @@ add_executable(AmalgamatedTestCompilation
   ${CATCH_DIR}/extras/catch_amalgamated_third_party.hpp
 )
 target_include_directories(AmalgamatedTestCompilation PRIVATE ${CATCH_DIR}/extras)
-# The amalgamated files hold the runner, which needs C++20.
+# The amalgamated files hold the runner, which needs C++17.
 target_compile_features(AmalgamatedTestCompilation PRIVATE cxx_std_17)
 
 add_test(NAME AmalgamatedFileTest COMMAND AmalgamatedTestCompilation --no-history)
diff --git a/tests/meson.build b/tests/meson.build
index 95556f06..6ec807d7 100644
--- a/tests/meson.build
+++ b/tests/meson.build
@@ -68,7 +68,7 @@ self_test = executable(
 
 test('SelfTest', self_test, args: ['--no-history'])
 
-# The Progmasoft tests need C++20; SelfTest keeps the C++ mode it has upstream.
+# The Progmasoft tests need C++17; SelfTest keeps the project's C++ mode.
 progmasoft_property_tests = executable(
   'ProgmasoftPropertyTests',
   [
diff --git a/xmake.lua b/xmake.lua
index 85a5b995..fd94efb8 100644
--- a/xmake.lua
+++ b/xmake.lua
@@ -3,7 +3,7 @@
 
 set_project("Catch3")
 set_version("0.3.0")
-set_languages("cxx14")
+set_languages("cxx17")
 set_warnings("all")
 
 local repository_root = os.projectdir()
@@ -15,11 +15,9 @@ includes("third_party/yyjson", "third_party/pugixml")
 
 -- The Catch2-compatible engine, the Catch3 runner, which replaced Catch2's
 -- session, command line and reporters, property testing and snapshots. The
--- library is C++20; the engine's headers still need only C++14 in the code
--- that includes them.
+-- library and the code that includes it need C++17.
 target("catch3")
     set_kind("static")
-    set_languages("cxx20")
     on_load(function(target)
         -- File I/O is restricted to Xmake's script domain, so generate here
         -- rather than while the declarative project file is being evaluated.
@@ -46,14 +44,12 @@ target("catch3")
 
 target("catch3_main")
     set_kind("static")
-    set_languages("cxx14")
     add_files("src/Progmasoft/Catch3/Internal/Main.cpp")
     add_deps("catch3")
     add_includedirs("src", generated_include, {public = true})
 
 target("ProgmasoftPropertyTests")
     set_kind("binary")
-    set_languages("cxx20")
     add_files(
         "tests/Progmasoft/Generators.tests.cpp",
         "tests/Progmasoft/Property.tests.cpp",