SQL Server 2008 R2 Readable Mirror

I know that SQL Server 2014 offers Availability Groups which provides this functionality, but I'm still stuck on SQL Server 2008 R2 for a while.

I recently came across this AWS whitepaper: http://ift.tt/1DL2sQA

I was confused by this chart on page 11: which seems to indicate that the mirror database can be used for reading (checks in the 'Readable Copy' feature column), just as it can when using Log Shipping, because it's been my experience that the mirror database cannot be used at all--it's only purpose is for failover.

The answer to this question: Database mirroring is limited to an original database seems to confirm my suspicions that the mirror database is NOT readable, though only in passing.

Is this whitepaper wrong, or are SQL Server 2008 R2 mirror databases indeed readable?

If they are, what does one need to do to do so, as attempting to connect in SSMS results in a window connected to the master database, and running USE [database] gives the following error:

Msg 954, Level 14, State 1, Line 1
The database "database" cannot be opened. It is acting as a mirror database.