code: @Override
      public void pushValidationGroupsToStack(String validationGroups)
      {
          if (_validationGroupsStack == null)
          {
              _validationGroupsStack = new LinkedList<String>();
          }
  
          _validationGroupsStack.addFirst(validationGroups);
      }
docs: Pushes validationGroups to the stack.
  @param validationGroups
  @since 2.0