docs: private AttributeDescr enabled(AttributeSupportBuilder<?> as) throws RecognitionException {
          AttributeDescrBuilder<?> attribute = null;
          try {
              // 'enabled'
              match(input,
                      DRL6Lexer.ID,
                      DroolsSoftKeywords.ENABLED,
                      null,
                      DroolsEditorType.KEYWORD);
              if (state.failed)
                  return null;
              if (state.backtracking == 0) {
                  attribute = helper.start((DescrBuilder<?, ?>) as,
                          AttributeDescrBuilder.class,
                          DroolsSoftKeywords.ENABLED);
              }
  
              boolean hasParen = input.LA(1) == DRL6Lexer.LEFT_PAREN;
              int first = input.index();
              if (hasParen) {
                  match(input,
                          DRL6Lexer.LEFT_PAREN,
                          null,
                          null,
                          DroolsEditorType.SYMBOL);
                  if (state.failed)
                      return null;
              }
  
              String value = conditionalExpression();
              if (state.failed)
                  return null;
  
              if (hasParen) {
                  match(input,
                          DRL6Lexer.RIGHT_PAREN,
                          null,
                          null,
                          DroolsEditorType.SYMBOL);
                  if (state.failed)
                      return null;
              }
              if (state.backtracking == 0) {
                  if (hasParen) {
                      value = input.toString(first,
                              input.LT(-1).getTokenIndex());
                  }
                  attribute.value(value);
                  attribute.type(AttributeDescr.Type.EXPRESSION);
              }
  
          } finally {
              if (attribute != null) {
                  helper.end(AttributeDescrBuilder.class,
                          attribute);
              }
          }
          return attribute != null ? attribute.getDescr() : null;
      }