upgrade/v2406-Developer-Upgrade-Guide.md

@@ -9,6 +9,34 @@
 
 [[_TOC_]]
 
+## Potential breaking changes
+
+### Finite Area
+
+The finite-area infrastructure has been revised to now have its own
+`objectRegistry` instead of simply riding onto of the polyMesh
+registry. Any existing finite-area code ***must*** be adjusted accordingly
+to ensure that the fields will be located properly.
+
+```
+areaScalarField h
+(
+    IOobject
+    (
+        "h",
+        runTime.timeName(),
+        // mesh_,        //<-- BAD this is the volume mesh!!
+        aMesh.thisDb(),  //<-- GOOD, works with v2312, v2406, ....
+        // aMesh,        //<-- OK to use area mesh directly (v2406)
+        IOobject::MUST_READ,
+        IOobject::AUTO_WRITE
+    ),
+    aMesh
+);
+
+```
+
+
 ## Deprecation and Removal
 
 ### Deprecated Methods