anchor.diff:    X-OCCI-Attribute: occi.compute.architechture="x86_64"
     X-OCCI-Attribute: occi.compute.architechture="x86_64", occi.compute.cores=2
   */
  -
  +//TODO output attribute header as JSON
   attribute_header:
     ATTR_HEADER attribute_attrs
   ;
   attribute_attrs:
  -  attribute_attr (',' attribute_attr)*
  +  attribute_attr (COMMA attribute_attr)*
   ;
   
   // ----------------------------------------
  
positive.code: // ----------------------------------------
  
  occi_header:
    ( category_header
    | link_header
    | attribute_header
    | location_header
    )+
    EOF
  
negative.code:   action-type      = type-identifier
    action-uri       = URL "?" "action=" term
  */
  //TODO action links spec to output JSON
  //TODO allow for 2 forms of Link headers
  //TODO allow for multiple links per line seperated by ','
  multiple_link_header
    : 'link TODO'
  ;
  link_header
    : LINK_HEADER  link_header_val
  ;
  link_header_val
    : link_path_attr rel_attr (self_attr | link_category_attr)* link_attributes_attr?
  ;
  link_path_attr:
    OPEN_PATH link_path_val CLOSE_PATH
  ;
  