...\<Base>
This sub-folder contains the source code and the Visual Studio .NET development files for the application base classes. These classes are provided to you in source code format so you have 100% of the source code needed for your application. You can modify the source code, create a new version of the compiled library and move the resulting .DLL (and .PDB) to the Bin folder of the application. This enables you to have different applications running different versions of the base classes.
Note: If you modify the base classes for your application, then you will need to merge the updates to the base classes in future versions.
The base class file system structure mirrors the base class namespaces. That is, files in the BaseClasses namespace are in:
...\BaseClasses\Base
Files in the BaseClasses.Web.UI namespace are in:
...\BaseClasses\Web\UI