Domain of Attributes for an Entity?

I am new to DBMS and was reading about the ER Model and entities-attributes. I found the following line in the book which I was reading: > The domain of Composite attributes is the cross product of domains of > component attributes. Which is fairly straight forward and intuitive. However, I was not able to understand the line following it: > The domain of Multi-valued attributes is a set of subsets of values > from the basic domain. I couldn't understand this line. I know Power set , which is set of all subsets of a set. Does this line mean, The domain is the power set of the basic domain set? I tried searching on the web before posting, but couldn't find any related literature/ explanation. A simple language explanation would help! Thank you!