During C# generation, each main object (class, interface, and so on) generates a source file with the .cs extension. Inner classifiers are generated in the source of the container classifier.
Using Directive
The using directive can appear at the beginning of the script of each generated file.
In PowerDesigner, you can define a using directive in the Script\Imports tab of the property sheet of a main object. You can type the using statement or use the Import Folder or Import Classifier tools in the Imports tab.
