xiaoyafeng,
Your node may be confusing to those following along at home. For those interested, the relavent synopses are packages, modules, and objects.

Unlike perl 5 which really only gave you one way to define a namespace (package), perl 6 will give you several which will help better define what that name space is doing. This is somewhat synonomous with the restriction of defining methods and functions in perl 5 with sub where perl 6 will have different keywords. Because they are defined with different keywords, they can have different behaviors. The same goes with the differences in packages, modules, and classes.

Update: Oh, and package is absolutely necessary if you intend to mix and match perl 5 and perl 6.