AppliedWebFeatures Element (Upgrade)
Supplies a list of Web site Features to be marked as "provisioned" for Web sites created in Microsoft SharePoint Foundation 2010. For example, an announcements list template of the previous version must be mapped (related) to its equivalent announcements Feature in the new version.
The AppliedWebFeatures element activates each feature, including running a Feature activating event handler, when the Web site is upgraded. This allows you to run custom code during upgrade, and implement custom features solely for the purpose of doing custom site transformation.
For an example of how this element is used, see Upgrade Definition schema.