code: public R visitVariable(VariableElement e, P p) {
          if (e.getKind() != ElementKind.RESOURCE_VARIABLE)
              return defaultAction(e, p);
          else
              return visitUnknown(e, p);
      }
docs: {@inheritDoc}
  
  This implementation calls {@code defaultAction}, unless the
  element is a {@code RESOURCE_VARIABLE} in which case {@code
  visitUnknown} is called.
  
  @param e {@inheritDoc}
  @param p {@inheritDoc}
  @return  the result of {@code defaultAction} or {@code visitUnknown}