code: public String getUUID() throws UnsupportedRepositoryOperationException, RepositoryException
     {
        checkValid();
  
        if (isNodeType(Constants.MIX_REFERENCEABLE))
        {
           return this.getInternalIdentifier();
        }
  
        throw new UnsupportedRepositoryOperationException("Node " + getPath() + " is not referenceable");
  
     }
docs: {@inheritDoc}