Difference between MultiSet and ExpressionSet class

Question

[wangshx]

ExpressionSet is very common and useful,here I have a question about the difference between the MultiSet class and ExpressionSet class.

The reference tells that

Container for high-throughput assays and experimental metadata. MutliSet is derived from eSet-class. MultiSet differs from ExpressionSet-class because MultiSet can contain any element(s) in assayData (ExpressionSet must have an element named exprs).

Does this mean that I can define multiple elements such as exprs1, exprs2...? Can I put different date types in each element? For example, exprs1 I store normalized gene expression matrix and exprs2 I store normalized gene-level Copy Number matrix?

I really wanna know is the different usage of the two classes and when should I use.