Unboxed Tuple in a single STG variable

Hello, Can an STG variable (Id) store a whole unboxed tuple value? Or is it required to decompose a returned unboxed value immediately by using an StgCase expression? If so, then is it correct that the STG variables can store values only from the following types: Addr, Float, Double, Int, Word, Ptr (for boxed values)? (and no multi-value values) Thanks, Csaba