diff --git a/definitions/region/README.md b/definitions/region/README.md
index 63e6e20e..43e733c8 100644
--- a/definitions/region/README.md
+++ b/definitions/region/README.md
@@ -142,6 +142,18 @@ Example:
 
 > Norway>Germany
 
+To represent data that refers to a flow or cost contribution of a region
+to a connection between two regions, the third contributing region name 
+can be combined with the bi-directional data using a `:` character before
+the bi-directional data (without spaces before/after that character).
+
+The third contributing region can be of **a different level of spatial detail**
+from the bi-directional data.
+
+Example:
+
+> Germany:France>Spain
+
 ## Parallel connections of directional data
 
 When timeseries data represents flows or capacity on one of several parallel