diff --git a/bacnet-stack/wp.h b/bacnet-stack/wp.h
index 141da5ad..a26100d9 100644
--- a/bacnet-stack/wp.h
+++ b/bacnet-stack/wp.h
@@ -39,13 +39,16 @@
 #include "bacdcode.h"
 #include "bacapp.h"
 
+/* write property can have application tagged data, or context tagged data,
+   or even complex data types (i.e. opening and closing tag around data).
+   It could also have more than one value.  */
 typedef struct BACnet_Write_Property_Data {
     BACNET_OBJECT_TYPE object_type;
     uint32_t object_instance;
     BACNET_PROPERTY_ID object_property;
     int32_t array_index;        /* use BACNET_ARRAY_ALL when not setting */
     BACNET_APPLICATION_DATA_VALUE value;
-    uint8_t priority;           /* use 0 if not setting the priority */
+    uint8_t priority;           /* use BACNET_NO_PRIORITY if no priority */
 } BACNET_WRITE_PROPERTY_DATA;
 
 #ifdef __cplusplus