::Within a XUL file, classes of elements are skinned with the definitions in the CSS file. However the definitions in the CSS file are just pointers to the bindings in the XBL. Bindings that are used to give the elements functionality or perhaps add or make change in their property. The design pattern used is indirection (Delegation pattern) where one object relies upon another to provide a specified set of functionality. In this case the CSS file relies on the bindings in the XBL file to provide it with definitions and functionalities for the elements.