The below diagram illustrates the relationship between Visualforce pages and Apex classes inside the SkyVisualEditor AppExchange package. Please refer to the SkyVisualEditor package for more details about interfaces to methods or classes.
Method of checking package：
In Salesforce, click Setup -> App Setup -> Installed Packages -> SkyVisualEditor
The Apex class extension functionality is used to enhance the server side processing with classes made by the customer (Extended Apex class in the diagram) referenced by pages made with SkyVisualEditor. For developing Apex, make Apex class directly on browser（in Salesforce Setup -> App setup -> Develop -> Apex classes） or use a development toolkit such as eclipse and deploy to Salesforce.