diff --git a/etc/bashrc b/etc/bashrc
index 99cfe44af0d7e5f0175c5a39ae6b3125c1d501c5..50df795c080f80fad94e8a04c0e10005c60aebb7 100644
--- a/etc/bashrc
+++ b/etc/bashrc
@@ -3,7 +3,7 @@
 # \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
 #  \\    /   O peration     |
 #   \\  /    A nd           | Copyright (C) 2011-2016 OpenFOAM Foundation
-#    \\/     M anipulation  | Copyright (C) 2016-2017 OpenCFD Ltd.
+#    \\/     M anipulation  | Copyright (C) 2016-2018 OpenCFD Ltd.
 #------------------------------------------------------------------------------
 # License
 #     This file is part of OpenFOAM, licensed under GNU General Public License
@@ -13,23 +13,21 @@
 #     etc/bashrc
 #
 # Description
-#     Set OpenFOAM environment for POSIX shell (eg, bash,dash,zsh,...)
-#     Source manually or from the ~/.profile or ~/.bashrc files.
+#     The OpenFOAM environment for POSIX shell (eg, bash,dash,zsh,...).
+#     Source manually or from the ~/.bashrc or ~/.profile files.
 #
-# Note
-#     Many environment variables can be overridden using a <prefs.sh> file
-#     from one of these locations:
-#     * user-specific:
-#         * ~/.OpenFOAM/$WM_PROJECT_VERSION
-#         * ~/.OpenFOAM
-#     * group-specific:
-#         * $WM_PROJECT_SITE/site/$WM_PROJECT_VERSION
-#         * $WM_PROJECT_SITE/site
-#     * general:
-#         * $WM_PROJECT_DIR/etc
+#     Many settings can be overridden using a <prefs.sh> file:
 #
-#     Any changes made to this bashrc file may be lost with the next upgrade.
+#       - Base values (eg, from system admin):
+#         -  $WM_PROJECT_DIR/etc/prefs.sh
 #
+#       - User or group values (first file found):
+#         -  ~/.OpenFOAM/$WM_PROJECT_VERSION/prefs.sh
+#         -  ~/.OpenFOAM/prefs.sh
+#         -  $WM_PROJECT_SITE/site/$WM_PROJECT_VERSION/prefs.sh
+#         -  $WM_PROJECT_SITE/site/prefs.sh
+#
+# Note: Changes made to this bashrc file may be lost with the next upgrade.
 #------------------------------------------------------------------------------
 
 export WM_PROJECT=OpenFOAM
@@ -52,8 +50,8 @@ FOAM_INST_DIR=$HOME/$WM_PROJECT
 export FOAM_INST_DIR
 unset rc
 
-# Default environment variables.
-# Can override with a <prefs.sh> file instead of editing below.
+# Configuration environment variables.
+# Should override via <prefs.sh> file instead of editing this file.
 
 # [WM_COMPILER_TYPE] - Compiler location:
 # = system | ThirdParty
@@ -61,7 +59,7 @@ export WM_COMPILER_TYPE=system
 
 # [WM_COMPILER] - Compiler:
 # = Gcc | Gcc4[8-9] | Gcc5[1-5] | Gcc6[1-4] | Gcc7[1-3] | Gcc8[1] | GccKNL |
-#   Clang | Clang3[8-9] | Clang[4-6]0 | Icc | IccKNL | Cray | Arm
+#   Clang | Clang3[7-9] | Clang[4-6]0 | Icc | IccKNL | Cray | Arm
 export WM_COMPILER=Gcc
 
 # [WM_ARCH_OPTION] - Memory addressing:
@@ -88,12 +86,15 @@ export WM_COMPILE_OPTION=Opt
 export WM_MPLIB=SYSTEMOPENMPI
 
 
-# [FOAM_SIGFPE] - Trapping of floating-point exceptions.
+#------------------------------------------------------------------------------
+# (legacy / advanced)
+#
+# [FOAM_SIGFPE] - Trap floating-point exceptions.
 #               - overrides the 'trapFpe' controlDict entry
 # = true | false
 #export FOAM_SIGFPE=true
 
-# [FOAM_SETNAN] - Memory initialisation as NaN
+# [FOAM_SETNAN] - Initialize memory with NaN
 #               - overrides the 'setNaN' controlDict entry
 # = true | false
 #export FOAM_SETNAN=false
@@ -129,10 +130,9 @@ export WM_PROJECT_USER_DIR=$HOME/$WM_PROJECT/$USER-$WM_PROJECT_VERSION
 # Load shell functions
 . $WM_PROJECT_DIR/etc/config.sh/functions
 
-# Override definitions via prefs, with 'other' first so the sys-admin
-# can provide base values independent of WM_PROJECT_SITE
-_foamEtc -mode=o  prefs.sh
-_foamEtc -mode=ug prefs.sh
+# Overrides via <prefs.sh>
+_foamEtc -mode=o  prefs.sh      # 1) other (system) values
+_foamEtc -mode=ug prefs.sh      # 2) user or group values
 
 # Evaluate command-line parameters and record settings for later.
 # These can be used to set/unset values, specify additional files etc.
diff --git a/etc/config.csh/compiler b/etc/config.csh/compiler
index 26d9cc084a00434cfbdbb3b57f34e1fa88345553..2083665f46ee430a5863069891c6e35b249c44d0 100644
--- a/etc/config.csh/compiler
+++ b/etc/config.csh/compiler
@@ -3,7 +3,7 @@
 # \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
 #  \\    /   O peration     |
 #   \\  /    A nd           | Copyright (C) 2016 OpenFOAM Foundation
-#    \\/     M anipulation  | Copyright (C) 2016-2017 OpenCFD Ltd.
+#    \\/     M anipulation  | Copyright (C) 2016-2018 OpenCFD Ltd.
 #------------------------------------------------------------------------------
 # License
 #     This file is part of OpenFOAM, licensed under GNU General Public License
@@ -73,6 +73,7 @@ case ThirdParty:
         set gcc_version=gcc-8.1.0
         breaksw
     case Clang:
+    case Clang37:
         set clang_version=llvm-3.7.1
         breaksw
     case Clang38:
diff --git a/etc/config.csh/settings b/etc/config.csh/settings
index dc47b2553982bff8d9d198e630e137c41e1c8ee6..85bbff458dbe2dcc8bc893b4252d327753665d96 100644
--- a/etc/config.csh/settings
+++ b/etc/config.csh/settings
@@ -106,9 +106,11 @@ case Linux:
 case Darwin:    # Presumably x86_64
     if (! $?WM_ARCH_OPTION ) setenv WM_ARCH_OPTION 64  # Default to 64-bit
     setenv WM_ARCH darwin64
+    setenv WM_CFLAGS "$WM_CFLAGS -m64 -Ddarwin"
+    setenv WM_CXXFLAGS "$WM_CXXFLAGS -m64 -Ddarwin"
     /bin/cat << INCOMPLETE
 ===============================================================================
-Operating system '$WM_ARCH' has incomplete support in this OpenFOAM release.
+Darwin support (clang only) is incomplete or untested in this OpenFOAM release.
 For further assistance, please contact www.OpenFOAM.com
 ===============================================================================
 INCOMPLETE
diff --git a/etc/config.sh/compiler b/etc/config.sh/compiler
index 08b306b2d1db45786caf3cdc05743273c65fb8a4..5c9c318dd16eee4919e536f82709346d18559851 100644
--- a/etc/config.sh/compiler
+++ b/etc/config.sh/compiler
@@ -3,7 +3,7 @@
 # \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
 #  \\    /   O peration     |
 #   \\  /    A nd           | Copyright (C) 2011-2016 OpenFOAM Foundation
-#    \\/     M anipulation  | Copyright (C) 2016-2017 OpenCFD Ltd.
+#    \\/     M anipulation  | Copyright (C) 2016-2018 OpenCFD Ltd.
 #------------------------------------------------------------------------------
 # License
 #     This file is part of OpenFOAM, licensed under GNU General Public License
@@ -71,7 +71,7 @@ ThirdParty)
     Gcc81)
         gcc_version=gcc-8.1.0
         ;;
-    Clang)
+    Clang | Clang37)
         clang_version=llvm-3.7.1
         ;;
     Clang38)
diff --git a/etc/config.sh/settings b/etc/config.sh/settings
index bb7d71a2c4e6ca55efc5f368a331024dcb327ca8..6b51ae3b051435a0efae3d0f0fb2b8d9515683f8 100644
--- a/etc/config.sh/settings
+++ b/etc/config.sh/settings
@@ -100,9 +100,11 @@ Linux)
 Darwin)     # Presumably x86_64
     : ${WM_ARCH_OPTION:=64}; export WM_ARCH_OPTION  # Default to 64-bit
     WM_ARCH=darwin64
+    export WM_CFLAGS="$WM_CFLAGS -m64 -Ddarwin"
+    export WM_CXXFLAGS="$WM_CXXFLAGS -m64 -Ddarwin"
     /bin/cat << INCOMPLETE 1>&2
 ===============================================================================
-Operating system '$WM_ARCH' has incomplete support in this OpenFOAM release.
+Darwin support (clang only) is incomplete or untested in this OpenFOAM release.
 For further assistance, please contact www.OpenFOAM.com
 ===============================================================================
 INCOMPLETE
diff --git a/etc/cshrc b/etc/cshrc
index db8ac55a7df55a1b3cc1e5ba70a7acb7af68ca87..1792541cdbde81c172d6bf2d025d941ffdfba274 100644
--- a/etc/cshrc
+++ b/etc/cshrc
@@ -13,23 +13,21 @@
 #     etc/cshrc
 #
 # Description
-#     Set OpenFOAM environment for C-shell (csh, tcsh).
-#     Source manually or from the ~/.login or ~/.cshrc files.
+#     The OpenFOAM environment for C-shell (csh, tcsh).
+#     Source manually or from the ~/.cshrc or ~/.login files.
 #
-# Note
-#     Many environment variables can be overridden using a <prefs.csh> file
-#     from one of these locations:
-#     * user-specific:
-#         * ~/.OpenFOAM/$WM_PROJECT_VERSION
-#         * ~/.OpenFOAM
-#     * group-specific:
-#         * $WM_PROJECT_SITE/site/$WM_PROJECT_VERSION
-#         * $WM_PROJECT_SITE/site
-#     * general:
-#         * $WM_PROJECT_DIR/etc
+#     Many settings can be overridden using a <prefs.csh> file:
 #
-#     Any changes made to this cshrc file may be lost with the next upgrade.
+#       - Base values (eg, from system admin):
+#         -  $WM_PROJECT_DIR/etc/prefs.csh
 #
+#       - User or group values (first file found):
+#         -  ~/.OpenFOAM/$WM_PROJECT_VERSION/prefs.csh
+#         -  ~/.OpenFOAM/prefs.csh
+#         -  $WM_PROJECT_SITE/site/$WM_PROJECT_VERSION/prefs.csh
+#         -  $WM_PROJECT_SITE/site/prefs.csh
+#
+# Note: Changes made to this cshrc file may be lost with the next upgrade.
 #------------------------------------------------------------------------------
 
 setenv WM_PROJECT OpenFOAM
@@ -49,8 +47,8 @@ setenv FOAM_INST_DIR `lsof +p $$ |& \
 # END OF (NORMAL) USER EDITABLE PART
 ################################################################################
 
-# Default environment variables.
-# Can override with a <prefs.sh> file instead of editing below.
+# Configuration environment variables.
+# Should override via <prefs.csh> file instead of editing this file.
 
 # [WM_COMPILER_TYPE] - Compiler location:
 # = system | ThirdParty
@@ -58,7 +56,7 @@ setenv WM_COMPILER_TYPE system
 
 # [WM_COMPILER] - Compiler:
 # = Gcc | Gcc4[8-9] | Gcc5[1-5] | Gcc6[1-4] | Gcc7[1-3] | Gcc8[1] | GccKNL |
-#   Clang | Clang3[8-9] | Clang[4-6]0 | Icc | IccKNL | Cray | Arm
+#   Clang | Clang3[7-9] | Clang[4-6]0 | Icc | IccKNL | Cray | Arm
 setenv WM_COMPILER Gcc
 
 # [WM_ARCH_OPTION] - Memory addressing:
@@ -85,12 +83,15 @@ setenv WM_COMPILE_OPTION Opt
 setenv WM_MPLIB SYSTEMOPENMPI
 
 
-# [FOAM_SIGFPE] - Trapping of floating-point exceptions.
+#------------------------------------------------------------------------------
+# (legacy / advanced)
+#
+# [FOAM_SIGFPE] - Trap floating-point exceptions.
 #               - overrides the 'trapFpe' controlDict entry
 # = true | false
 #setenv FOAM_SIGFPE true
 
-# [FOAM_SETNAN] - Memory initialisation as NaN
+# [FOAM_SETNAN] - Initialize memory with NaN
 #               - overrides the 'setNaN' controlDict entry
 # = true | false
 #setenv FOAM_SETNAN false
@@ -139,10 +140,9 @@ setenv WM_PROJECT_USER_DIR $HOME/$WM_PROJECT/$LOGNAME-$WM_PROJECT_VERSION
 # Load shell "functions" (actually aliases)
 source $WM_PROJECT_DIR/etc/config.csh/functions
 
-# Override definitions via prefs, with 'other' first so the sys-admin
-# can provide base values independent of WM_PROJECT_SITE
-_foamEtc -mode=o  prefs.csh
-_foamEtc -mode=ug prefs.csh
+# Overrides via <prefs.csh>
+_foamEtc -mode=o  prefs.csh     # 1) other (system) systems
+_foamEtc -mode=ug prefs.csh     # 2) user or group settings
 
 # Evaluate command-line parameters and record settings for later.
 # These can be used to set/unset values, specify additional files etc.