diff --git a/applications/test/sort/Test-sortList.cxx b/applications/test/sort/Test-sortList.cxx
index 907f6436c9..1269c2cb8b 100644
--- a/applications/test/sort/Test-sortList.cxx
+++ b/applications/test/sort/Test-sortList.cxx
@@ -296,7 +296,7 @@ int main(int argc, char *argv[])
             (
                 strings,
                 order,
-                stringOps::natural_sort::less<string>(strings)
+                stringOps::natural_sort::list_less(strings)
             );
             Info<< "natural sortedOrder: " << flatOutput(order) << endl;
         }
@@ -321,7 +321,7 @@ int main(int argc, char *argv[])
             ///  sortable = hashed.toc();
             ///  sortable.sort
             ///  (
-            ///      stringOps::natural_sort::less<string>(sortable)
+            ///      stringOps::natural_sort::list_less(sortable)
             ///  );
             ///  Info<< nl << "natural:" << sortable << endl;
 
@@ -329,7 +329,7 @@ int main(int argc, char *argv[])
             ///  sortable = hashed.toc();
             ///  sortable.sort
             ///  (
-            ///      stringOps::natural_sort::greater<string>(sortable)
+            ///      stringOps::natural_sort::list_greater(sortable)
             ///  );
             ///  Info<< nl << "natural:" << sortable << endl;
         }
diff --git a/src/OpenFOAM/db/IOstreams/memory/memoryStreamBuffer.H b/src/OpenFOAM/db/IOstreams/memory/memoryStreamBuffer.H
index 446053a890..5c49b1d5b5 100644
--- a/src/OpenFOAM/db/IOstreams/memory/memoryStreamBuffer.H
+++ b/src/OpenFOAM/db/IOstreams/memory/memoryStreamBuffer.H
@@ -38,6 +38,7 @@ Description
 #include "DynamicList.H"
 
 #include <memory>
+#include <string_view>
 #include <string>
 #include <type_traits>
 
diff --git a/src/OpenFOAM/db/dictionary/dictionary.H b/src/OpenFOAM/db/dictionary/dictionary.H
index 67f771e3d2..38ded49d1d 100644
--- a/src/OpenFOAM/db/dictionary/dictionary.H
+++ b/src/OpenFOAM/db/dictionary/dictionary.H
@@ -113,6 +113,7 @@ SeeAlso
 #include "label.H"
 #include "scalar.H"
 #include "regExpFwd.H"
+#include "Switch.H"
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
diff --git a/src/OpenFOAM/db/error/messageStream.H b/src/OpenFOAM/db/error/messageStream.H
index e07345bb05..0f55064928 100644
--- a/src/OpenFOAM/db/error/messageStream.H
+++ b/src/OpenFOAM/db/error/messageStream.H
@@ -55,6 +55,8 @@ SourceFiles
 
 #include "label.H"
 #include "word.H"
+
+#include <string_view>
 #include <string>
 #include <iostream>
 
diff --git a/src/OpenFOAM/global/debug/simpleObjectRegistry.H b/src/OpenFOAM/global/debug/simpleObjectRegistry.H
index 5823c5a516..a7fc5a4139 100644
--- a/src/OpenFOAM/global/debug/simpleObjectRegistry.H
+++ b/src/OpenFOAM/global/debug/simpleObjectRegistry.H
@@ -40,6 +40,7 @@ SourceFiles
 
 #include "Dictionary.H"
 #include "simpleRegIOobject.H"
+#include <string_view>
 #include <string>
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
diff --git a/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.C b/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.C
index dd39a58954..b9eecd144f 100644
--- a/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.C
+++ b/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.C
@@ -333,7 +333,7 @@ Foam::fileMonitor& Foam::fileOperation::monitor() const
 
 void Foam::fileOperation::mergeTimes
 (
-    const instantList& extraTimes,
+    const UList<instant>& extraTimes,
     const word& constantName,
     instantList& times
 )
diff --git a/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.H b/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.H
index bd19e08c25..27e931ef02 100644
--- a/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.H
+++ b/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.H
@@ -198,8 +198,10 @@ protected:
         //- Merge two times
         static void mergeTimes
         (
-            const instantList& extraTimes,
+            const UList<instant>& extraTimes,
+            //! The "constant" name
             const word& constantName,
+            //! [in,out] Updated with any extra times
             instantList& times
         );
 
@@ -870,7 +872,13 @@ public:
             ) const;
 
             //- Get sorted list of times
-            virtual instantList findTimes(const fileName&, const word&) const;
+            virtual instantList findTimes
+            (
+                //! The directory to search
+                const fileName& directory,
+                //! The "constant" name
+                const word& constantName = "constant"
+            ) const;
 
             //- Find time instance where IOobject is located.
             //- The name of the IOobject can be empty, in which case only the
diff --git a/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.H b/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.H
index 37f49fc1ed..c68ea352dc 100644
--- a/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.H
+++ b/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.H
@@ -748,7 +748,13 @@ public:
         // Other
 
             //- Get sorted list of times
-            virtual instantList findTimes(const fileName&, const word&) const;
+            virtual instantList findTimes
+            (
+                //! The directory to search
+                const fileName& directory,
+                //! The "constant" name
+                const word& constantName = "constant"
+            ) const;
 
             //- Find time instance where IOobject is located.
             //- The name of the IOobject can be empty, in which case only the
diff --git a/src/OpenFOAM/include/addAllRegionOptions.H b/src/OpenFOAM/include/addAllRegionOptions.H
index 67e10b234e..fb9eced092 100644
--- a/src/OpenFOAM/include/addAllRegionOptions.H
+++ b/src/OpenFOAM/include/addAllRegionOptions.H
@@ -11,7 +11,10 @@ License
     This file is part of OpenFOAM, distributed under GPL-3.0-or-later.
 
 Description
-    Add multi-region command-line options: -allRegions, -regions, -region
+    Add multi-region command-line options:
+      -allRegions | -all-regions
+      -regions
+      -region
 
 Required Classes
     - Foam::argList
@@ -24,10 +27,10 @@ See Also
 {
     Foam::argList::addBoolOption
     (
-        "all-regions",
+        "allRegions",
         "Use all regions in regionProperties"
     );
-    Foam::argList::addOptionCompat("all-regions", { "allRegions", -2506 });
+    Foam::argList::addOptionCompat("allRegions", { "all-regions", 0 });
 
     Foam::argList::addOption
     (
diff --git a/src/OpenFOAM/include/getAllRegionOptions.H b/src/OpenFOAM/include/getAllRegionOptions.H
index 887646b9d6..dcea9facdc 100644
--- a/src/OpenFOAM/include/getAllRegionOptions.H
+++ b/src/OpenFOAM/include/getAllRegionOptions.H
@@ -45,12 +45,19 @@ See Also
 
 wordList regionNames;
 {
-    // Local alias
-    auto& names = regionNames;
     // Exit or fallback if nothing matches
     constexpr bool exitOnNoMatches = true;
 
-    if (args.found("all-regions"))
+    // Local aliases
+    auto& names = regionNames;
+    const auto& fallback = Foam::polyMesh::defaultRegion;
+
+    if
+    (
+        // Handle both here (independent of which is an alias)
+        args.found("all-regions")
+     || args.found("allRegions")
+    )
     {
         names =
         (
@@ -81,11 +88,11 @@ wordList regionNames;
     {
         select.uniq();  // Normally a no-op
 
-        if (select.size() == 1 && select.front().isLiteral())
+        if (select.size() == 1 && select[0].isLiteral())
         {
             // Identical to -region NAME
             names.resize(1);
-            names.front() = select.front();
+            names[0] = select[0];
         }
         else if (select.size())
         {
@@ -116,12 +123,12 @@ wordList regionNames;
                     }
                     else
                     {
-                        InfoErr<< "... ignoring and using default region"
+                        InfoErr
+                            << "... ignoring and using default region"
                             << nl << endl;
 
-                        // Arbitrary fallback, but can handle this further on
                         names.resize(1);
-                        names.front() = Foam::polyMesh::defaultRegion;
+                        names[0] = fallback;
                     }
                 }
                 else
@@ -160,7 +167,7 @@ wordList regionNames;
                 else
                 {
                     names.resize(1);
-                    names.front() = Foam::polyMesh::defaultRegion;
+                    names[0] = fallback;
 
                     InfoErr
                         << "Warning: No regionProperties, "
@@ -169,17 +176,30 @@ wordList regionNames;
             }
         }
     }
-    else if (args.found("region"))
+    else
     {
+        // Single region option or fallback
         names.resize(1);
-        names.front() = args.get<word>("region");
+        auto& name = names[0];
+
+        if
+        (
+            !args.readIfPresent("region", name)
+        )
+        {
+            name = fallback;
+        }
     }
 
-    // Fallback to defaultRegion
+    // Final sanity checks and/or fallback
     if (names.empty())
     {
         names.resize(1);
-        names.front() = Foam::polyMesh::defaultRegion;
+        names[0] = fallback;
+    }
+    else if (names.size() == 1 && names[0].empty())
+    {
+        names[0] = fallback;
     }
 }
 
diff --git a/src/OpenFOAM/primitives/bools/Switch/Switch.H b/src/OpenFOAM/primitives/bools/Switch/Switch.H
index ddef797909..af8effc2f1 100644
--- a/src/OpenFOAM/primitives/bools/Switch/Switch.H
+++ b/src/OpenFOAM/primitives/bools/Switch/Switch.H
@@ -43,6 +43,9 @@ SourceFiles
 #include "bool.H"
 #include "stdFoam.H"
 
+#include <string_view>
+#include <string>
+
 // Avoid any pre-processor conflicts with enum names
 #undef FALSE
 #undef TRUE
diff --git a/src/OpenFOAM/primitives/strings/lists/CStringList.H b/src/OpenFOAM/primitives/strings/lists/CStringList.H
index fd24374be1..1e88bc84a2 100644
--- a/src/OpenFOAM/primitives/strings/lists/CStringList.H
+++ b/src/OpenFOAM/primitives/strings/lists/CStringList.H
@@ -60,6 +60,7 @@ Description
 #include <utility>    // std::initializer_list
 #include <vector>
 #include <string_view>
+#include <string>
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
diff --git a/src/OpenFOAM/primitives/strings/lists/SubStrings.H b/src/OpenFOAM/primitives/strings/lists/SubStrings.H
index eb98de37ee..dcb8b6b943 100644
--- a/src/OpenFOAM/primitives/strings/lists/SubStrings.H
+++ b/src/OpenFOAM/primitives/strings/lists/SubStrings.H
@@ -37,6 +37,7 @@ Description
 
 #include <regex>    // For std::ssub_match
 #include <memory>
+#include <string_view>
 #include <string>
 #include <vector>
 
diff --git a/src/OpenFOAM/primitives/strings/regex/regExpCxx.H b/src/OpenFOAM/primitives/strings/regex/regExpCxx.H
index d2f288e1be..49e523d89f 100644
--- a/src/OpenFOAM/primitives/strings/regex/regExpCxx.H
+++ b/src/OpenFOAM/primitives/strings/regex/regExpCxx.H
@@ -69,6 +69,7 @@ SourceFiles
 #define Foam_regExpCxx_H
 
 #include <regex>
+#include <string_view>
 #include <string>
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
diff --git a/src/OpenFOAM/primitives/strings/string/string.H b/src/OpenFOAM/primitives/strings/string/string.H
index 878028e6b8..14d0de250b 100644
--- a/src/OpenFOAM/primitives/strings/string/string.H
+++ b/src/OpenFOAM/primitives/strings/string/string.H
@@ -54,6 +54,7 @@ SourceFiles
 #include "Hasher.H"
 #include <cstdlib>
 #include <cstring>
+#include <string_view>
 #include <string>
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
diff --git a/src/OpenFOAM/primitives/strings/stringOps/stringOpsSort.H b/src/OpenFOAM/primitives/strings/stringOps/stringOpsSort.H
index 3574b3e6b6..6c169f3f93 100644
--- a/src/OpenFOAM/primitives/strings/stringOps/stringOpsSort.H
+++ b/src/OpenFOAM/primitives/strings/stringOps/stringOpsSort.H
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2017 OpenCFD Ltd.
+    Copyright (C) 2017-2025 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -46,85 +46,106 @@ namespace Foam
 namespace stringOps
 {
 
-    //- 'Natural' compare for C-strings
-    //  Uses algorithm and code from Jan-Marten Spit <jmspit@euronet.nl>
-    //
-    //  In the 'natural' comparison, strings are compared alphabetically
-    //  and numerically. Thus 'file010.txt' sorts after 'file2.txt'
-    //
-    //  \param s1 left string
-    //  \param s2 right string
+//- 'Natural' compare for C-strings
+//  Uses algorithm and code from Jan-Marten Spit <jmspit@euronet.nl>
+//
+//  In the 'natural' comparison, strings are compared alphabetically
+//  and numerically. Thus 'file010.txt' sorts after 'file2.txt'
+//
+//  \param s1 left string
+//  \param s2 right string
+//  \return -1 when s1 < s2, 0 when s1 == s2, 1 when s1 > s2
+int natstrcmp(const char* s1, const char* s2);
+
+
+//- Encapsulation of natural order sorting for algorithms
+struct natural_sort
+{
+    //- Natural compare for std::string
     //  \return -1 when s1 < s2, 0 when s1 == s2, 1 when s1 > s2
-    int natstrcmp(const char* s1, const char* s2);
-
-
-    //- Encapsulation of natural order sorting for algorithms
-    struct natural_sort
+    static inline int compare
+    (
+        const std::string& s1,
+        const std::string& s2
+    )
     {
-        //- Natural compare for std::string
-        //  \return -1 when s1 < s2, 0 when s1 == s2, 1 when s1 > s2
-        static inline int compare
-        (
-            const std::string& s1,
-            const std::string& s2
-        )
-        {
-            return natstrcmp(s1.data(), s2.data());
-        }
+        return stringOps::natstrcmp(s1.data(), s2.data());
+    }
 
-        //- Default (forward) natural sorting
+    //- Natural compare two strings for a less-than relationship
+    static inline bool less
+    (
+        const std::string& s1,
+        const std::string& s2
+    )
+    {
+        return (natural_sort::compare(s1, s2) < 0);
+    }
+
+    //- Natural compare two strings for a greater-than relationship
+    static inline bool greater
+    (
+        const std::string& s1,
+        const std::string& s2
+    )
+    {
+        return (natural_sort::compare(s1, s2) > 0);
+    }
+
+    //- Default (forward) natural sorting
+    bool operator()(const std::string& s1, const std::string& s2) const
+    {
+        return (natural_sort::compare(s1, s2) < 0);
+    }
+
+    //- Reverse natural sorting
+    struct reverse
+    {
+        //- Reverse natural sorting
         bool operator()(const std::string& s1, const std::string& s2) const
         {
-            return natural_sort::compare(s1, s2) < 0;
+            return (natural_sort::compare(s1, s2) > 0);
         }
-
-        //- Reverse natural sorting
-        struct reverse
-        {
-            //- Reverse natural sorting
-            bool operator()(const std::string& s1, const std::string& s2) const
-            {
-                return natural_sort::compare(s1, s2) > 0;
-            }
-        };
-
-
-        //- A list compare binary predicate for natural sort
-        template<class T>
-        struct less
-        {
-            const UList<T>& values;
-
-            less(const UList<T>& list)
-            :
-                values(list)
-            {}
-
-            bool operator()(const label a, const label b) const
-            {
-                return natural_sort::compare(values[a], values[b]) < 0;
-            }
-        };
-
-
-        //- A list compare binary predicate for reverse natural sort
-        template<class T>
-        struct greater
-        {
-            const UList<T>& values;
-
-            greater(const UList<T>& list)
-            :
-                values(list)
-            {}
-
-            bool operator()(const label a, const label b) const
-            {
-                return natural_sort::compare(values[a], values[b]) > 0;
-            }
-        };
     };
 
+
+    //- A UList compare binary predicate for natural sort
+    template<class T>
+    struct list_less
+    {
+        const UList<T>& values;
+
+        list_less(const UList<T>& list) noexcept
+        :
+            values(list)
+        {}
+
+        bool operator()(label a, label b) const
+        {
+            return (natural_sort::compare(values[a], values[b]) < 0);
+        }
+    };
+
+
+    //- A Ulist compare binary predicate for reverse natural sort
+    template<class T>
+    struct list_greater
+    {
+        const UList<T>& values;
+
+        list_greater(const UList<T>& list) noexcept
+        :
+            values(list)
+        {}
+
+        bool operator()(label a, label b) const
+        {
+            return (natural_sort::compare(values[a], values[b]) > 0);
+        }
+    };
+};
+
+
 } // End namespace stringOps
 } // End namespace Foam
 
diff --git a/src/fileFormats/vtk/file/foamVtkSeriesWriter.C b/src/fileFormats/vtk/file/foamVtkSeriesWriter.C
index 0950fe2a59..7a2a85c5c2 100644
--- a/src/fileFormats/vtk/file/foamVtkSeriesWriter.C
+++ b/src/fileFormats/vtk/file/foamVtkSeriesWriter.C
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2018-2023 OpenCFD Ltd.
+    Copyright (C) 2018-2025 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -64,13 +64,17 @@ namespace Foam
     //   2. natural sort (name)
     struct seriesLess
     {
-        bool operator()(const fileNameInstant a, const fileNameInstant b) const
+        template<class StringType>
+        bool operator()
+        (
+            const Instant<StringType>& a,
+            const Instant<StringType>& b
+        ) const
         {
             scalar val = compareOp<scalar>()(a.value(), b.value());
             if (val == 0)
             {
-                return
-                    stringOps::natural_sort::compare(a.name(), b.name()) < 0;
+                return stringOps::natural_sort::less(a.name(), b.name());
             }
             return val < 0;
         }
@@ -78,7 +82,7 @@ namespace Foam
 
 
     // Check if value is less than upper, with some tolerance.
-    static inline bool lessThan(const scalar& val, const scalar& upper)
+    static inline bool lessThan(scalar val, scalar upper)
     {
         return (val < upper && Foam::mag(val - upper) > ROOTVSMALL);
     }
diff --git a/src/finiteArea/include/addAllFaRegionOptions.H b/src/finiteArea/include/addAllFaRegionOptions.H
index cefac98abc..9b203ebba0 100644
--- a/src/finiteArea/include/addAllFaRegionOptions.H
+++ b/src/finiteArea/include/addAllFaRegionOptions.H
@@ -12,7 +12,9 @@ License
 
 Description
     Add multi-region command-line options:
-    -all-area-regions, -area-regions, -area-region
+      -allAreas | -all-area-regions
+      -area-regions
+      -area-region
 
 Required Classes
     - Foam::argList
@@ -25,9 +27,10 @@ See Also
 {
     Foam::argList::addBoolOption
     (
-        "all-area-regions",
+        "allAreas",
         "Use all regions in finite-area regionProperties"
     );
+    Foam::argList::addOptionCompat("allAreas", { "all-area-regions", 0 });
 
     Foam::argList::addOption
     (
@@ -41,8 +44,11 @@ See Also
     (
         "area-region",
         "name",
-        "Specify area-mesh region. Eg, -region shell"
+        "Specify area-mesh region. Eg, -area-region shell"
     );
+
+    // TBD:
+    //? Foam::argList::addOptionCompat("area-region", { "areaRegion", 0 });
 }
 
 
diff --git a/src/finiteArea/include/getAllFaRegionOptions.H b/src/finiteArea/include/getAllFaRegionOptions.H
index 7e456a6d00..bd1cd32991 100644
--- a/src/finiteArea/include/getAllFaRegionOptions.H
+++ b/src/finiteArea/include/getAllFaRegionOptions.H
@@ -15,7 +15,7 @@ Description
     (-all-area-regions | -area-regions | -area-region)
 
 Priority
-    1. -all-area-regions
+    1. -all-area-regions (-allAreas)
     2. -area-regions = specify multiple area regions to select,
         or a single area region
     3. -area-region = specify a single area region
@@ -46,12 +46,19 @@ See Also
 
 wordList areaRegionNames;
 {
-    // Local alias
-    auto& names = areaRegionNames;
     // Exit or fallback if nothing matches
     constexpr bool exitOnNoMatches = false;
 
-    if (args.found("all-area-regions"))
+    // Local aliases
+    auto& names = areaRegionNames;
+    const auto& fallback = Foam::polyMesh::defaultRegion;
+
+    if
+    (
+        // Handle both here (independent of which is an alias)
+        args.found("all-area-regions")
+     || args.found("allAreas")
+    )
     {
         names =
         (
@@ -78,16 +85,20 @@ wordList areaRegionNames;
     else if
     (
         wordRes select;
-        args.readListIfPresent<wordRe>("area-regions", select)
+        (
+            // Handle both here (independent of which is an alias)
+            args.readListIfPresent<wordRe>("area-regions", select)
+         || args.readListIfPresent<wordRe>("areaRegions", select)
+        )
     )
     {
         select.uniq();  // Normally a no-op
 
-        if (select.size() == 1 && select.front().isLiteral())
+        if (select.size() == 1 && select[0].isLiteral())
         {
             // Identical to -area-region NAME
             names.resize(1);
-            names.front() = select.front();
+            names[0] = select[0];
         }
         else if (select.size())
         {
@@ -119,12 +130,12 @@ wordList areaRegionNames;
                     }
                     else
                     {
-                        InfoErr<< "... ignoring and using default region"
+                        InfoErr
+                            << "... ignoring and using default region"
                             << nl << endl;
 
-                        // Arbitrary fallback, but can handle this further on
                         names.resize(1);
-                        names.front() = Foam::polyMesh::defaultRegion;
+                        names[0] = fallback;
                     }
                 }
                 else
@@ -162,7 +173,7 @@ wordList areaRegionNames;
                 else
                 {
                     names.resize(1);
-                    names.front() = Foam::polyMesh::defaultRegion;
+                    names[0] = fallback;
 
                     InfoErr
                         << "Warning: No finite-area regionProperties, "
@@ -171,17 +182,32 @@ wordList areaRegionNames;
             }
         }
     }
-    else if (args.found("area-region"))
+    else
     {
+        // Single region option or fallback
         names.resize(1);
-        names.front() = args.get<word>("area-region");
+        auto& name = names[0];
+
+        if
+        (
+            // Handle both here (independent of which is an alias)
+            !args.readIfPresent("area-region", name)
+         && !args.readIfPresent("areaRegion", name)
+        )
+        {
+            name = fallback;
+        }
     }
 
-    // Fallback to defaultRegion
+    // Final sanity checks and/or fallback
     if (names.empty())
     {
         names.resize(1);
-        names.front() = Foam::polyMesh::defaultRegion;
+        names[0] = fallback;
+    }
+    else if (names.size() == 1 && names[0].empty())
+    {
+        names[0] = fallback;
     }
 }