We've looked at two language constructs you can use in the module descriptor--requiring modules and exporting packages. Together, they give you sufficient control over the interface of your modules and they address the two main goals of modularity--reliable configuration and strong encapsulation. However, in many real-world situations, you might sometimes find that these two alone are not enough to achieve certain things you want to do. For example, you may want to export a package from a module, only for it to be consumed by a certain other module, and not for public consumption. To handle many such special cases, the module system has some powerful features that we'll take a look at in this part of the chapter.