code: protected boolean isValidAction(Action action) {
          return getActions().contains(action) || Action.cancel.equals(action);
      }
docs: Returns true if the <code>action</code> is available in the current stage.
  The {@link Action#cancel cancel} action is always allowed. To define the
  available actions use the <code>addActionAvailable</code> method.
  
  @param action
  The action to check if it is available.
  @return True if the action is available for the current stage.