anchor.diff:      ( multi_attr2 = attribute_attr_name
         {$attributes += ", \"" + $multi_attr2.attribute_name + "\"";}
       )+
  +;
  +action_attr returns [String actions]
  +  : CAT_ATTR_SEP ACTION_ATTR VAL_ASSIGN QUOTE action_val QUOTE
  +    {$actions = $action_val.actions;}
  +;
  +action_val returns [String actions]
  +  : single_attr = action_uri
  +    {$actions = "\"" + $single_attr.action + "\"";}
  +  | multi_attr1 = action_uri {$actions = "\"" + $multi_attr1.action + "\"";}
  +    (
  +      multi_attr2 = action_uri {$actions += ", \"" + $multi_attr2.action + "\"";}
  +    )+
  +
  +;
  +action_uri returns [String action]
  +  : URI
  +    {$action = $URI.text;}
   ;
   // ----------------------------------------
   // -------------- Link Header -------------
  
positive.code:       attributes="occi.storage.size occi.storage.state";
        actions="http://schemas.ogf.org/occi/infrastructure/storage/action#resize ...";
  */
  //TODO implement action attribute
  multiple_category_header
    : CATEGORY_HEADER category_header_val (COMMA category_header_val)+
  ;
  category_header returns [String category]
    : CATEGORY_HEADER category_header_val
      {$category = "{\"category\":{" + $category_header_val.category + "}}"; }
  ;
  category_header_val returns [String category]
    : term_attr scheme_attr class_attr (title_attr | rel_attr | location_attr | cat_attributes_attr)*
      {
        $category =
        "\"term\":\"" + $term_attr.term + "\", " +
  
negative.code: 
  occi_header:
    (
    //Nice-to-have: merge these 2 rules
      multiple_category_header
    | category_header
  
    //Nice-to-have: merge these 2 rules
    | multiple_link_header
    | link_header
  
  