code: private void checkVersionable( AbstractJcrNode node ) throws UnsupportedRepositoryOperationException, RepositoryException {
          if (!node.isNodeType(JcrMixLexicon.VERSIONABLE)) {
              throw new UnsupportedRepositoryOperationException(JcrI18n.requiresVersionable.text());
          }
      }
docs: Throw an {@link UnsupportedRepositoryOperationException} if the node is not versionable (i.e.,
  isNodeType(JcrMixLexicon.VERSIONABLE) == false).
  
  @param node the node to check
  @throws UnsupportedRepositoryOperationException if <code>!isNodeType({@link JcrMixLexicon#VERSIONABLE})</code>
  @throws RepositoryException if an error occurs reading the node types for this node