5. The XML virtual machine as recited in claim 1 , wherein defining a set of runtime objects for executing an application includes registering a notifier object that represents a trigger encountered in application code with a trigger event bus, the registered notifier object identifying at least a user interface component and an event type that will activate the corresponding trigger.
5. The XML virtual machine as recited in claim 1 , wherein defining a set of runtime objects for executing an application includes registering a notifier object that represents a trigger encountered in application code with a trigger event bus, the registered notifier object identifying at least a user interface component and an event type that will activate the corresponding trigger. 8. The XML virtual machine as recited in claim 5 , wherein the XML virtual machine is configured to use a single copy of application code for more than one application instance that is executing.