A component has another identifier called UUID (Universal Unique ID), which application developers rarely need.

UUID is used by components and Client Engine to manipulate DOM at the browser and to communicate with the server. More precisely, the id attribute of a DOM element at the client is UUID.

UUID is generated automatically when a component is created. It is immutable, except the identifiers of components for representing HTML tags.

HTML relevant components handle UUID different from other set of components: UUID is the same as ID. If you change ID of a HTML relevant component, UUID will be changed accordingly. Therefore, old JavaScript codes and servlets will remain to work without any modification.