code: private boolean isValidDoclet() {
          if (!getClass().getName().equals(TOOLKIT_DOCLET_NAME)) {
              messages.error("doclet.Toolkit_Usage_Violation",
                  TOOLKIT_DOCLET_NAME);
              return false;
          }
          return true;
      }
docs: Verify that the only doclet that is using this toolkit is
  {@value #TOOLKIT_DOCLET_NAME}.