anchor.diff:        return;
       }
   
  +    if (_isLinkOnReferenceAppendix(contentInput.value, link)) {
  +      return;
  +    }
  +
       _applyAutoLink(selectionText, link);
  +  }
  +
  +  /**
  +   * two cases:
  +   *
  +   * 1. user manually editing appendix section, when he paste into this section,
  +   *    we should not process it
  +   * 2. user paste a link in textarea, but the link already in appendix, we ignore this case too.
  +   */
  +  bool _isLinkOnReferenceAppendix(String fullText, String link) {
  +    var existRefs = ReferenceAppendix.tryParse(fullText);
  +    return existRefs.any((ref) => ref.url == link);
     }
   
     /**
  
positive.code:       var pastedTextLength = contentInput.value.length - (initialText.length - selectionLength);
        var end = pasteAtIndex + pastedTextLength;
        var pastedText = contentInput.value.substring(pasteAtIndex, end);
        _onTextPasted(selectionText, pastedText);
      });
  
      // clipboardData only support in chrome, give up
  
negative.code:   }
  
    void _onTextPasted(String selectionText, String text) {
      // if user selected url and paste new link, we don't process
      // it because user just replace it's old link
      if (_PURE_LINK_REGEX.hasMatch(selectionText)) {
        return;
      }
  
      //detect only pure link text
      var match = _PURE_LINK_REGEX.firstMatch(text);
      if (match == null) {
  