Every XML element in the configuration files is read and processed by a corresponding Java class during startup. This class does not implement the actual user interface element, but a builder for that element. This allows to implement dynamic controls whose state is updated at runtime. If no java_class is specified for an element, a default builder class is used for creating the user interface control. New dynamic controls can be created by implementing the corresponding Java interface and specifying the implementation class for the control in the XML files. The following table lists all available builder interfaces and their default implementations.