anchor.diff:  // ----------------------------------------
   
   occi_header:
  -    category_header
  +  ( category_header
     | link_header
     | attribute_header
     | location_header
  +  )+
   ;
   
   // ----------------------------------------
  
positive.code: URI: ('http://' | 'https://') TOKEN;
  TOKEN: ('a'..'z' | 'A'..'Z') ('a'..'z' | 'A'..'Z')*;
  DIGIT: '0'..'9'+;
  WS: (' ' | '\t'){$channel = HIDDEN};
negative.code:       attributes="occi.storage.size occi.storage.state";
        actions="http://schemas.ogf.org/occi/infrastructure/storage/action#resize ...";
  */
  //TODO allow for multiple categories per line seperated by ','
  category_header:
    CATEGORY_HEADER category_header_val
  ;
  category_header_val:
    term scheme class (title | rel | location | attributes)*
  ;
  term:
    TOKEN
  ;
  