diff --git a/applications/test/exprTraits/Make/files b/applications/test/exprTraits/Make/files
new file mode 100644
index 0000000000..6ae37c355d
--- /dev/null
+++ b/applications/test/exprTraits/Make/files
@@ -0,0 +1,3 @@
+Test-exprTraits.C
+
+EXE = $(FOAM_USER_APPBIN)/Test-exprTraits
diff --git a/applications/test/exprTraits/Make/options b/applications/test/exprTraits/Make/options
new file mode 100644
index 0000000000..18e6fe47af
--- /dev/null
+++ b/applications/test/exprTraits/Make/options
@@ -0,0 +1,2 @@
+/* EXE_INC = */
+/* EXE_LIBS = */
diff --git a/applications/test/exprTraits/Test-exprTraits.C b/applications/test/exprTraits/Test-exprTraits.C
new file mode 100644
index 0000000000..3dee3b436f
--- /dev/null
+++ b/applications/test/exprTraits/Test-exprTraits.C
@@ -0,0 +1,79 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | www.openfoam.com
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+    Copyright (C) 2021 OpenCFD Ltd.
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM, distributed under GPL-3.0-or-later.
+
+Description
+    Basic tests of expression traits
+
+\*---------------------------------------------------------------------------*/
+
+#include "IOstreams.H"
+#include "ITstream.H"
+#include "exprTraits.H"
+#include "uLabel.H"
+#include "error.H"
+#include "stringList.H"
+
+using namespace Foam;
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+template<class T>
+void printTraits()
+{
+    const auto typeCode = exprTypeTraits<T>::value;
+
+    Info<< "type " << pTraits<T>::typeName
+        << " code:" << int(typeCode)
+        << " name:" << exprTypeTraits<T>::name;
+
+    if (pTraits<T>::typeName != word(exprTypeTraits<T>::name))
+    {
+        Info<< " (UNSUPPORTED)";
+    }
+
+    Info << endl;
+}
+
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+int main()
+{
+    Info<< nl << "Traits:" << nl;
+
+    printTraits<word>();
+    printTraits<string>();
+    printTraits<bool>();
+    printTraits<label>();
+    printTraits<scalar>();
+    printTraits<vector>();
+    printTraits<tensor>();
+    printTraits<symmTensor>();
+    printTraits<sphericalTensor>();
+
+    const auto getName = nameOp<expressions::valueTypeCode>();
+
+    Info<< nl;
+
+    Info<< "Name of typeCode: "
+        << Foam::name(expressions::valueTypeCode::type_scalar) << nl;
+
+    Info<< "Name of typeCode: "
+        << getName(expressions::valueTypeCode::type_bool) << nl;
+
+
+    Info<< nl << "Done" << nl;
+    return 0;
+}
+
+
+// ************************************************************************* //
diff --git a/applications/utilities/preProcessing/setExprFields/setExprFields.C b/applications/utilities/preProcessing/setExprFields/setExprFields.C
index 673767fe08..402b6679f5 100644
--- a/applications/utilities/preProcessing/setExprFields/setExprFields.C
+++ b/applications/utilities/preProcessing/setExprFields/setExprFields.C
@@ -53,15 +53,15 @@ Note
 
 using namespace Foam;
 
-using FieldAssociation = expressions::volumeExpr::FieldAssociation;
+using FieldAssociation = expressions::FieldAssociation;
 
 word fieldGeoType(const FieldAssociation geoType)
 {
     switch (geoType)
     {
-        case FieldAssociation::VOLUME_DATA : return "cells"; break;
-        case FieldAssociation::SURFACE_DATA : return "faces"; break;
         case FieldAssociation::POINT_DATA : return "points"; break;
+        case FieldAssociation::FACE_DATA : return "faces"; break;
+        case FieldAssociation::VOLUME_DATA : return "cells"; break;
         default: break;
     }
 
@@ -356,6 +356,7 @@ void evaluate
                 if (ptr)
                 {
                     conditionField = ptr->internalField();
+                    // VOLUME_DATA
                     break;
                 }
             }
@@ -366,7 +367,7 @@ void evaluate
                 if (ptr)
                 {
                     conditionField = ptr->internalField();
-                    conditionDataType = FieldAssociation::SURFACE_DATA;
+                    conditionDataType = FieldAssociation::FACE_DATA;
                     break;
                 }
             }
diff --git a/src/OpenFOAM/Make/files b/src/OpenFOAM/Make/files
index 6b2f614607..7e4850fc44 100644
--- a/src/OpenFOAM/Make/files
+++ b/src/OpenFOAM/Make/files
@@ -163,6 +163,8 @@ $(expr)/exprResult/exprResultStoredStack.C
 $(expr)/exprString/exprString.C
 $(expr)/exprTools/exprTools.C
 
+$(expr)/traits/exprTraits.C
+
 $(expr)/exprDriver/exprDriver.C
 $(expr)/exprDriver/exprDriverFields.C
 $(expr)/exprDriver/exprDriverIO.C
diff --git a/src/OpenFOAM/expressions/exprDriver/exprDriver.H b/src/OpenFOAM/expressions/exprDriver/exprDriver.H
index 72dcb73e52..408c0f7fb6 100644
--- a/src/OpenFOAM/expressions/exprDriver/exprDriver.H
+++ b/src/OpenFOAM/expressions/exprDriver/exprDriver.H
@@ -59,10 +59,12 @@ SourceFiles
 #ifndef expressions_exprDriver_H
 #define expressions_exprDriver_H
 
-#include "exprString.H"
 #include "exprResult.H"
+#include "exprString.H"
+#include "exprTraits.H"
 #include "pointField.H"
 #include "primitiveFields.H"
+#include "objectRegistry.H"
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
diff --git a/src/OpenFOAM/expressions/exprResult/exprResult.H b/src/OpenFOAM/expressions/exprResult/exprResult.H
index 90083ae906..3e9d19f6bc 100644
--- a/src/OpenFOAM/expressions/exprResult/exprResult.H
+++ b/src/OpenFOAM/expressions/exprResult/exprResult.H
@@ -57,12 +57,8 @@ SourceFiles
 #ifndef expressions_exprResult_H
 #define expressions_exprResult_H
 
-#include "vector.H"
-#include "tensor.H"
-#include "sphericalTensor.H"
-#include "symmTensor.H"
+#include "exprTraits.H"
 #include "dimensionedType.H"
-#include "IOField.H"
 #include "runTimeSelectionTables.H"
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
diff --git a/src/OpenFOAM/expressions/traits/exprFieldAssociation.H b/src/OpenFOAM/expressions/traits/exprFieldAssociation.H
new file mode 100644
index 0000000000..f7970973e1
--- /dev/null
+++ b/src/OpenFOAM/expressions/traits/exprFieldAssociation.H
@@ -0,0 +1,62 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | www.openfoam.com
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+    Copyright (C) 2019-2021 OpenCFD Ltd.
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+Class
+    Foam::expressions::FieldAssociation
+
+Description
+    The field association for mesh (patch/volume) values.
+
+\*---------------------------------------------------------------------------*/
+
+#ifndef expressions_FieldAssociation_H
+#define expressions_FieldAssociation_H
+
+namespace Foam
+{
+namespace expressions
+{
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+enum FieldAssociation : unsigned char
+{
+    NO_DATA = 0,         //!< No data
+    POINT_DATA = 1,      //!< Point data
+    FACE_DATA = 2,       //!< Face data
+    VOLUME_DATA = 4      //!< Volume data
+};
+
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+} // End namespace expressions
+} // End namespace Foam
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+#endif
+
+// ************************************************************************* //
diff --git a/src/OpenFOAM/expressions/traits/exprTraits.C b/src/OpenFOAM/expressions/traits/exprTraits.C
new file mode 100644
index 0000000000..2f4dda37a4
--- /dev/null
+++ b/src/OpenFOAM/expressions/traits/exprTraits.C
@@ -0,0 +1,96 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | www.openfoam.com
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+    Copyright (C) 2021 OpenCFD Ltd.
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+\*---------------------------------------------------------------------------*/
+
+#include "exprTraits.H"
+
+// * * * * * * * * * * * * * * * Global Functions  * * * * * * * * * * * * * //
+
+Foam::expressions::valueTypeCode
+Foam::expressions::valueTypeCodeOf(const word& dataTypeName)
+{
+    #undef  stringToTypeCode
+    #define stringToTypeCode(Type)                                  \
+                                                                    \
+    if (dataTypeName == exprTypeTraits<Type>::name)                 \
+    {                                                               \
+        return expressions::valueTypeCode::type_##Type;             \
+    }
+
+    if (!dataTypeName.empty())
+    {
+        stringToTypeCode(bool);
+        stringToTypeCode(label);
+        stringToTypeCode(scalar);
+        stringToTypeCode(vector);
+        stringToTypeCode(tensor);
+        stringToTypeCode(sphericalTensor);
+        stringToTypeCode(symmTensor);
+    }
+    #undef stringToTypeCode
+
+    return expressions::valueTypeCode::INVALID;
+}
+
+
+Foam::word Foam::name(const expressions::valueTypeCode typeCode)
+{
+    #undef  case_typeCodeToString
+    #define case_typeCodeToString(Type)                             \
+                                                                    \
+    case expressions::valueTypeCode::type_##Type :                  \
+    {                                                               \
+        return exprTypeTraits<Type>::name;                          \
+    }
+
+    switch (typeCode)
+    {
+        case expressions::valueTypeCode::NONE :
+        {
+            return "none";
+        }
+
+        case expressions::valueTypeCode::INVALID :
+        {
+            // ie, ""
+            break;
+        }
+
+        case_typeCodeToString(bool);
+        case_typeCodeToString(label);
+        case_typeCodeToString(scalar);
+        case_typeCodeToString(vector);
+        case_typeCodeToString(tensor);
+        case_typeCodeToString(sphericalTensor);
+        case_typeCodeToString(symmTensor);
+    }
+    #undef case_typeCodeToString
+
+    return word();
+}
+
+
+// ************************************************************************* //
diff --git a/src/OpenFOAM/expressions/traits/exprTraits.H b/src/OpenFOAM/expressions/traits/exprTraits.H
new file mode 100644
index 0000000000..6c2173eea8
--- /dev/null
+++ b/src/OpenFOAM/expressions/traits/exprTraits.H
@@ -0,0 +1,160 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | www.openfoam.com
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+    Copyright (C) 2021 OpenCFD Ltd.
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+Class
+    Foam::exprTypeTraits
+
+Description
+    Simple type identifiers for polymorphic expression values.
+
+    The definitions are similar to std::integral_constant in that they
+    provide value, value_type (and name).
+
+\*---------------------------------------------------------------------------*/
+
+#ifndef expressions_exprTraits_H
+#define expressions_exprTraits_H
+
+// Regular field types
+#include "label.H"
+#include "scalar.H"
+#include "vector.H"
+#include "sphericalTensor.H"
+#include "symmTensor.H"
+#include "tensor.H"
+#include "word.H"
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+namespace Foam
+{
+namespace expressions
+{
+
+//- An enumeration of known and expected expression value types.
+//  Do not rely on the enumeration values for any direct coding.
+//
+//  \note NONE use used when initializing types, whereas INVALID is used
+//  for unsupported types (never as a stored type).
+//  This avoids false positives when testing.
+//
+//  Except NONE and INVALID, the enumerations will mostly not be used
+//  directly, but through exprTypeTraits :: value
+
+enum class valueTypeCode : unsigned char
+{
+    NONE = 0,               //!< No type, or default initialized type
+    INVALID,                //!< Invalid/unknown/error type
+
+    // Rank 0 types
+    type_bool,              //!< Type is 'bool'
+    type_label,             //!< Type is 'label'
+    type_scalar,            //!< Type is 'scalar'
+
+    // Rank 1 types
+    type_vector,            //!< Type is 'vector'
+
+    // Rank 2 types
+    type_sphericalTensor,   //!< Type is 'sphericalTensor'
+    type_symmTensor,        //!< Type is 'symmTensor'
+    type_tensor             //!< Type is 'tensor'
+};
+
+
+// Global Functions
+
+//- From string to valueTypeCode (if any)
+valueTypeCode valueTypeCodeOf(const word& dataTypeName);
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+} // End namespace expressions
+
+
+/*---------------------------------------------------------------------------*\
+                       Class exprTypeTraits Declaration
+\*---------------------------------------------------------------------------*/
+
+// Generic enumerated traits is INVALID (unknown)
+template<class Type>
+struct exprTypeTraits
+{
+    typedef Type value_type;
+    static constexpr const char* const name = "";
+    static constexpr
+        ::Foam::expressions::valueTypeCode value =
+        ::Foam::expressions::valueTypeCode::INVALID;
+};
+
+
+#undef  defineExprTypeTraits
+#define defineExprTypeTraits(Type, Name)                                      \
+    template<>                                                                \
+    struct exprTypeTraits<Type>                                               \
+    {                                                                         \
+        typedef Type value_type;                                              \
+        static constexpr const char* const name = #Name;                      \
+        static constexpr                                                      \
+            ::Foam::expressions::valueTypeCode value =                        \
+            ::Foam::expressions::valueTypeCode::type_##Name;                  \
+    };
+
+
+// Define with "name" to match regular pTraits typeName
+defineExprTypeTraits(bool, bool);
+defineExprTypeTraits(::Foam::label, label);
+defineExprTypeTraits(::Foam::scalar, scalar);
+defineExprTypeTraits(::Foam::vector, vector);
+defineExprTypeTraits(::Foam::tensor, tensor);
+defineExprTypeTraits(::Foam::sphericalTensor, sphericalTensor);
+defineExprTypeTraits(::Foam::symmTensor, symmTensor);
+
+#undef defineExprTypeTraits
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+//- A word representation of a valueTypeCode. Empty for INVALID
+word name(const expressions::valueTypeCode typeCode);
+
+
+//- A word representation of a valueTypeCode. Empty for INVALID
+template<>
+struct nameOp<expressions::valueTypeCode>
+{
+    word operator()(const expressions::valueTypeCode typeCode) const
+    {
+        return Foam::name(typeCode);
+    }
+};
+
+// No IOstream Operators for valueTypeCode at the moment (Nov 2021)
+
+} // End namespace Foam
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+#endif
+
+// ************************************************************************* //
diff --git a/src/OpenFOAM/primitives/pTraits/pTraits.H b/src/OpenFOAM/primitives/traits/pTraits.H
similarity index 100%
rename from src/OpenFOAM/primitives/pTraits/pTraits.H
rename to src/OpenFOAM/primitives/traits/pTraits.H
diff --git a/src/finiteVolume/expressions/patch/patchExprDriver.H b/src/finiteVolume/expressions/patch/patchExprDriver.H
index 55a907ffa3..25ab0469d3 100644
--- a/src/finiteVolume/expressions/patch/patchExprDriver.H
+++ b/src/finiteVolume/expressions/patch/patchExprDriver.H
@@ -67,6 +67,7 @@ SourceFiles
 
 #include "patchExprFwd.H"
 #include "fvExprDriver.H"
+#include "exprFieldAssociation.H"
 #include "Enum.H"
 #include "volFields.H"
 #include "surfaceFields.H"
diff --git a/src/finiteVolume/expressions/patch/patchExprDriverI.H b/src/finiteVolume/expressions/patch/patchExprDriverI.H
index b4ae95c4ea..aed253621f 100644
--- a/src/finiteVolume/expressions/patch/patchExprDriverI.H
+++ b/src/finiteVolume/expressions/patch/patchExprDriverI.H
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2019 OpenCFD Ltd.
+    Copyright (C) 2019-2021 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -36,10 +36,10 @@ inline Foam::label Foam::expressions::patchExpr::parseDriver::size
     {
         case FieldAssociation::POINT_DATA :
             return patch_.patch().nPoints();
-            break;
-        case FieldAssociation::SURFACE_DATA :
+
+        case FieldAssociation::FACE_DATA :
             return patch_.patch().size();
-            break;
+
         default:
             break;
     }
diff --git a/src/finiteVolume/expressions/patch/patchExprFwd.H b/src/finiteVolume/expressions/patch/patchExprFwd.H
index 5682b896fb..cd04bcbf6c 100644
--- a/src/finiteVolume/expressions/patch/patchExprFwd.H
+++ b/src/finiteVolume/expressions/patch/patchExprFwd.H
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2019 OpenCFD Ltd.
+    Copyright (C) 2019-2021 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -52,16 +52,6 @@ union scanToken;
 //- Static debugging option
 extern int debug;
 
-
-//- The field association for patch expressions (mutually exclusive)
-enum FieldAssociation : unsigned char
-{
-    NO_DATA = 0,         //!< No data
-    POINT_DATA = 1,      //!< Point data
-    SURFACE_DATA = 2     //!< Surface data
-};
-
-
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
 } // End namespace patchExpr
@@ -73,6 +63,7 @@ typedef patchExpr::parseDriver patchExprDriver;
 
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
 } // End namespace expressions
 } // End namespace Foam
 
diff --git a/src/finiteVolume/expressions/volume/volumeExprDriver.H b/src/finiteVolume/expressions/volume/volumeExprDriver.H
index 5237a38853..985b3f27e2 100644
--- a/src/finiteVolume/expressions/volume/volumeExprDriver.H
+++ b/src/finiteVolume/expressions/volume/volumeExprDriver.H
@@ -84,6 +84,7 @@ SourceFiles
 
 #include "volumeExprFwd.H"
 #include "fvExprDriver.H"
+#include "exprFieldAssociation.H"
 #include "volFields.H"
 #include "surfaceFields.H"
 #include "pointFields.H"
@@ -126,7 +127,7 @@ protected:
         bool isLogical_;
 
         //- A volume/surface/point field
-        enum FieldAssociation fieldGeoType_;
+        expressions::FieldAssociation fieldGeoType_;
 
         //- The result dimensions
         dimensionSet resultDimension_;
@@ -259,37 +260,37 @@ public:
         //- The result type-name.
         //  Normally volScalarField, surfaceVectorField etc,
         //  but Scalar is modified for logical as volScalarField etc
-        const word& resultType() const
+        const word& resultType() const noexcept
         {
             return resultType_;
         }
 
         //- The geometric field association
-        FieldAssociation fieldAssociation() const
+        FieldAssociation fieldAssociation() const noexcept
         {
             return fieldGeoType_;
         }
 
         //- A logical (bool-like) field. Actually stored as a scalar.
-        bool isLogical() const
+        bool isLogical() const noexcept
         {
             return isLogical_;
         }
 
         //- A volume field
-        bool isVolumeData() const
+        bool isVolumeData() const noexcept
         {
             return fieldGeoType_ == FieldAssociation::VOLUME_DATA;
         }
 
         //- A surface field
-        bool isSurfaceData() const
+        bool isFaceData() const noexcept
         {
-            return fieldGeoType_ == FieldAssociation::SURFACE_DATA;
+            return fieldGeoType_ == FieldAssociation::FACE_DATA;
         }
 
         //- A point field
-        bool isPointData() const
+        bool isPointData() const noexcept
         {
             return fieldGeoType_ == FieldAssociation::POINT_DATA;
         }
diff --git a/src/finiteVolume/expressions/volume/volumeExprDriverI.H b/src/finiteVolume/expressions/volume/volumeExprDriverI.H
index 2863f0ba1e..8c6d00bb50 100644
--- a/src/finiteVolume/expressions/volume/volumeExprDriverI.H
+++ b/src/finiteVolume/expressions/volume/volumeExprDriverI.H
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2019 OpenCFD Ltd.
+    Copyright (C) 2019-2021 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -36,13 +36,13 @@ inline Foam::label Foam::expressions::volumeExpr::parseDriver::size
     {
         case FieldAssociation::POINT_DATA :
             return mesh_.nPoints();
-            break;
-        case FieldAssociation::SURFACE_DATA :
+
+        case FieldAssociation::FACE_DATA :
             return mesh_.nInternalFaces();
-            break;
+
         case FieldAssociation::VOLUME_DATA :
             return mesh_.nCells();
-            break;
+
         default:
             break;
     }
diff --git a/src/finiteVolume/expressions/volume/volumeExprDriverTemplates.C b/src/finiteVolume/expressions/volume/volumeExprDriverTemplates.C
index d16a946d35..60c54f2d40 100644
--- a/src/finiteVolume/expressions/volume/volumeExprDriverTemplates.C
+++ b/src/finiteVolume/expressions/volume/volumeExprDriverTemplates.C
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2019 OpenCFD Ltd.
+    Copyright (C) 2019-2021 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -102,7 +102,7 @@ void Foam::expressions::volumeExpr::parseDriver::setResult
     // Characteristics
     resultType_ = pTraits<fieldType>::typeName;
     isLogical_ = logical;
-    fieldGeoType_ = SURFACE_DATA;
+    fieldGeoType_ = FACE_DATA;
 
     // Always strip out dimensions?
     if (!resultDimension_.dimensionless())
diff --git a/src/finiteVolume/expressions/volume/volumeExprFwd.H b/src/finiteVolume/expressions/volume/volumeExprFwd.H
index 1a5df406c4..bff30718d1 100644
--- a/src/finiteVolume/expressions/volume/volumeExprFwd.H
+++ b/src/finiteVolume/expressions/volume/volumeExprFwd.H
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2019 OpenCFD Ltd.
+    Copyright (C) 2019-2021 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -40,6 +40,7 @@ namespace expressions
 {
 namespace volumeExpr
 {
+
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
 // Forward Declarations
@@ -51,16 +52,6 @@ union scanToken;
 //- Static debugging option
 extern int debug;
 
-//- The field association for volume expressions (mutually exclusive)
-enum FieldAssociation : unsigned char
-{
-    NO_DATA = 0,         //!< No data
-    POINT_DATA = 1,      //!< Point data
-    SURFACE_DATA = 2,    //!< Surface data
-    VOLUME_DATA = 3      //!< Volume data
-};
-
-
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
 } // End namespace volumeExpr
diff --git a/src/surfMesh/polySurface/polySurface.H b/src/surfMesh/polySurface/polySurface.H
index 9fb5479b80..45cdff160f 100644
--- a/src/surfMesh/polySurface/polySurface.H
+++ b/src/surfMesh/polySurface/polySurface.H
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2019-2020 OpenCFD Ltd.
+    Copyright (C) 2019-2021 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -77,9 +77,9 @@ public:
     enum FieldAssociation
     {
         NO_DATA = 0,            //!< No associated data
-        FACE_DATA = 0x1,        //!< Data associated with faces
-        POINT_DATA = 0x2,       //!< Data associated with points
-        FACE_POINT_DATA = 0x3   //!< Data associated with faces and points
+        FACE_DATA = 1,          //!< Data associated with faces
+        POINT_DATA = 2,         //!< Data associated with points
+        FACE_OR_POINT_DATA = 3  //!< Data associated with faces or points
     };