Convenience functions are methods that do something which would normally take several Motif calls to set up. Fallback resources provide protection against the possibility that an application defaults file is not installed. They are ignored if the app-defaults fiel or any other explicit resource settings are found. A widget class has its own resources as well as inherets resources from its superclass. The names of a widgets resources can be found in tables and the most useful resources are used in examples.
Most resources have reasonable default values.
Resources can be specified in a user resource specification in an X resource file. Resources can be specified at widget creation time. The shell is an extremely simple manager. In this case the button is made as the only child of the top level shell. The first argument to the XtVaAppInitialize is the address of an application context which is a structure that Xt uses to manage some internal data associated with an application.