A database created by a more recent version of SQL Server cannot be attached or restored to an earlier version. This restriction is simply because an older version cannot know about file format changes that were introduced in the newer release.
If you attempt to attach a database to an earlier version, you will get SQL Server error 948 with the internal version numbers listed in the error message text. For example, the following error occurs if you try to attach a SQL Server 2008 R2 database to a SQL Server 2008 server:
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