anchor.diff:  */
   attribute_header returns [String attribute_header]
     : ATTR_HEADER attribute_attrs
  -    {$attribute_header = "{\"attributes\":{"+$attribute_attrs.attribute_attrs+"}}";}
  +    {$attribute_header = "\"attributes\":{"+$attribute_attrs.attribute_attrs+"}";}
   ;
   attribute_attrs returns [String attribute_attrs]
     : attribute_attr
  
positive.code: 
  occi_request returns [String request]
    : occi_header
      {$request = "[" + $occi_header.header + "]";}
    | multi_val1 = occi_header
      {$request = "[" + $multi_val1.header;}
      (
        multi_val2 = occi_header
        {$request += ", " + $multi_val2.header;}
      )+
      {$request += "]";}
  ;
  occi_header returns [String header]
    : category_header {$header = $category_header.category;}
  
negative.code: 
  link_header returns [String link_header]
    : LINK_HEADER single_val = link_header_val
      {$link_header = "\"link\":{" + $single_val.link_header_val + "}";}
  
    | LINK_HEADER multi_val1 = link_header_val
      {$link_header = "\"link\" : [{"+$multi_val1.link_header_val + "}";}
      (
        COMMA multi_val2 = link_header_val
        {$link_header += ", {"+$multi_val2.link_header_val + "}";}
      )+
      {$link_header += "]";}
  ;
  link_header_val returns [String link_header_val]
    : OPEN_PATH link_path_val CLOSE_PATH rel_attr
  