Mysterious system table: master.sys.sysdbreg

Have you ever seen the system table, "master.sys.sysdbreg" in your SQL Server. I've seen this unintentionally while working on something else. I was analyzing a query plan in XML view. Suddenly I saw this system table. See below portion of execution plan.

XML view of execution plan

Then I immediately opened a new query window to see the data of this system table and it gave me an error. Then I did googling and found the below links which state more information of it. 


The Resource Database
System Base Tables


So it is actually belongs to "mssqlsystemresource" hidden database. I was able to see the data through DAC (Dedicated Administrator Connection). The data of this system table somewhat similar to "sys.sysdatabases". Additionally it shows the resource database which is normally not shown in "sys.sysdatabases".