[2877] Document new column

Describe the value of the column in the NSEC3 case.

src/lib/datasrc/database.h

@@ -137,7 +137,8 @@ public:
         DEL_TYPE = 1, ///< The RRType of the record (A/NS/TXT etc.)
         DEL_RDATA = 2, ///< Full text representation of the record's RDATA
         DEL_RNAME = 3, ///< As DEL_NAME, but with the labels of domain name
-                       ///< in reverse order (eg. org.example.).
+                       ///< in reverse order (eg. org.example.). With NSEC3,
+                       ///< it is the same as DEL_NAME.
         DEL_PARAM_COUNT = 4 ///< Number of parameters
     };