diff --git a/osi_common.proto b/osi_common.proto
index 7db75ca7a..a4e62071a 100644
--- a/osi_common.proto
+++ b/osi_common.proto
@@ -245,7 +245,11 @@ message ExternalReference
     // reverse domain name notation with lower-case type field
     // is recommended to guarantee unique and interoperable identification.
     //
-    optional string type = 2;    
+    // \rules
+    // is_set
+    // \endrules
+    //
+    optional string type = 2;
     
     // The external identifier reference value.
     //
diff --git a/osi_detectedobject.proto b/osi_detectedobject.proto
index fb4e4e62b..3ea53c4e0 100644
--- a/osi_detectedobject.proto
+++ b/osi_detectedobject.proto
@@ -325,6 +325,10 @@ message DetectedMovingObject
         // \note This field is mandatory if the \c CandidateMovingObject::type
         // is \c MovingObject::TYPE_VEHICLE .
         //
+        // \rules
+        // check_if this.type is_equal_to 2 else do_check is_set
+        // \endrules
+        //
         optional MovingObject.VehicleClassification vehicle_classification = 3;
 
         // Pedestrian head pose for behavior prediction. Describes the head
@@ -339,6 +343,10 @@ message DetectedMovingObject
         // \note This field is mandatory if the \c CandidateMovingObject.type is
         // \c MovingObject::TYPE_PEDESTRIAN
         //
+        // \rules
+        // check_if this.type is_equal_to 3 else do_check is_set
+        // \endrules
+        //
         // \par Reference:
         //
         // [1] Patton, K. T. & Thibodeau, G. A. (2015). <em>Anatomy & Physiology</em>. 9th Edition. Elsevier. Missouri, U.S.A. ISBN 978-0-323-34139-4. p. 1229.
@@ -358,6 +366,10 @@ message DetectedMovingObject
         // \note This field is mandatory if the \c CandidateMovingObject::type
         // is \c MovingObject::TYPE_PEDESTRIAN
         //
+        // \rules
+        // check_if this.type is_equal_to 3 else do_check is_set
+        // \endrules
+        //
         // \par Reference:
         // [1] Patton, K. T. & Thibodeau, G. A. (2015). <em>Anatomy & Physiology</em>. 9th Edition. Elsevier. Missouri, U.S.A. ISBN 978-0-323-34139-4. p. 1229.
         //
diff --git a/osi_trafficcommand.proto b/osi_trafficcommand.proto
index 61c62a9b6..d8763b430 100644
--- a/osi_trafficcommand.proto
+++ b/osi_trafficcommand.proto
@@ -142,6 +142,10 @@ message TrafficAction
         // \note This id must be unique within all traffic command
         // messages exchanged with one traffic participant.
         //
+        // \rules
+        // is_set
+        // \endrules
+        //
         optional Identifier action_id = 1;
     }