1. A system for providing a model for system-wide application extension, said system comprising: an application server that executes on one or more microprocessors, wherein the application server includes a plurality of applications , wherein each application is associated with an application type, and includes application code and application configuration data; a first shared library that contains fragment code, fragment configuration data, and a first tag, wherein the first shared library is identified by the application server as an auto-ref library using the first tag; wherein when a particular application of said plurality of applications is deployed as a particular deployed application on the application server, the application server causes the particular deployed application to automatically reference the auto-ref library unless the application type associated with the particular application is excluded by the auto-ref library; wherein when referencing the auto-ref library, the fragment code and the fragment configuration data of the auto-ref library are automatically merged into the application code and application configuration data of the particular application at deployment time without replacing any conflicting application code, and wherein conflicting application code and application configuration data of the particular application are used without modification in the particular deployed application; a second shared library that contains superseding code, superseding configuration data, and a second tag, different than the first tag, wherein the second shared library is identified by the application server as a superseding library using the second tag; wherein when the particular application is deployed on the application server as the particular deployed application, the application server causes the particular deployed application to automatically reference the superseding library unless the application type associated with the particular application is excluded by the superseding library; and wherein when referencing the superseding library, the superseding code and the superseding configuration data override the application code of the particular application, such that conflicting application code and configuration data of the particular application is replaced by the superseding code and superseding configuration data in the particular deployed application, and wherein application code and application configuration data of the particular application that is not replaced by the superseding library is used without modification in the particular deployed application.