Report Server - SQL Server - Mixing versions

Hi,

I'm using RS 2012 SP1 standard evaluation on SQL Server 2012 SP1 also.

since the configuration is very flexible and I can easily specify a diferent database, I would like to know if I can use an older version of SQL Server for the RS database?

Can it be SQL Server 2008 version? Can it be a SQL Server Express edition?

Many thanks,

DD