code: public String createUniqueId(FacesContext context, String seed) {
          if (seed != null) {
              return UIViewRoot.UNIQUE_ID_PREFIX + seed;
          } else {
              Integer i = (Integer) getStateHelper().get(PropertyKeys.lastId);
              int lastId = ((i != null) ? i : 0);
              getStateHelper().put(PropertyKeys.lastId,  ++lastId);
              return UIViewRoot.UNIQUE_ID_PREFIX + lastId;
          }
      }
docs: <p>Generate an identifier for a component. The identifier
  will be prefixed with UNIQUE_ID_PREFIX, and will be unique
  within this UIViewRoot. Optionally, a unique seed value can
  be supplied by component creators which should be
  included in the generated unique id.</p>
  
  @param context FacesContext
  @param seed an optional seed value - e.g. based on the position of the component in the VDL-template
  @return a unique-id in this component-container