diff --git a/Subdivision_method_3/doc/Subdivision_method_3/Concepts/PQQMask_3.h b/Subdivision_method_3/doc/Subdivision_method_3/Concepts/PQQMask_3.h
index 994e3156660..617057ffccc 100644
--- a/Subdivision_method_3/doc/Subdivision_method_3/Concepts/PQQMask_3.h
+++ b/Subdivision_method_3/doc/Subdivision_method_3/Concepts/PQQMask_3.h
@@ -66,7 +66,9 @@ void vertex_node(vertex_descriptor vd, Point_3& pt);
 /*!
 
 computes the edge-point `ept` and the vertex-point `vpt`
-based on the neighborhood of the border edge `hd`.
+based on the neighborhood of the border edge of `hd`. `hd` is not
+a border halfedge (its opposite is) and `vpt` corresponds to the
+target vertex of `hd`.
 */
 void border_node(halfedge_descriptor hd, Point_3& ept, Point_3& vpt);
 
diff --git a/Subdivision_method_3/doc/Subdivision_method_3/Concepts/PTQMask_3.h b/Subdivision_method_3/doc/Subdivision_method_3/Concepts/PTQMask_3.h
index 7c02c35d833..c15a6e5099e 100644
--- a/Subdivision_method_3/doc/Subdivision_method_3/Concepts/PTQMask_3.h
+++ b/Subdivision_method_3/doc/Subdivision_method_3/Concepts/PTQMask_3.h
@@ -55,9 +55,10 @@ of the vertex `vd`.
 void vertex_node(vertex_descriptor vd, Point_3& pt);
 
 /*!
-
 computes the edge-point `ept` and the vertex-point `vpt`
-based on the neighborhood of the border edge `hd`.
+based on the neighborhood of the border edge of `hd`. `hd` is not
+a border halfedge (its opposite is) and `vpt` corresponds to the
+target vertex of `hd`.
 */
 void border_node(halfedge_descriptor hd, Point_3& ept, Point_3& vpt);