+One big difference to L<Rose::DB/do_transaction> is the return code
+handling. If a transaction is already active then C<with_transcation>
+simply returns the result of calling C<$code_ref> as-is.
+
+Otherwise the return value depends on the result of the underlying
+transaction. If the transaction fails then C<undef> is returned in
+scalar context and an empty list in list context. If the transaction
+succeeds then the return value of C<$code_ref> is returned preserving
+context.
+
+So if you want to differentiate between "transaction failed" and
+"succeeded" then your C<$code_ref> should never return C<undef>
+itself.
+