anchor.diff:     NO_READVERTISE
   ;
   
  +srt_no_retain
  +:
  +   NO_RETAIN
  +;
  +
   srt_passive
   :
      PASSIVE
  
positive.code:    | srt_next_hop
     | srt_next_table
     | srt_no_readvertise
     | srt_passive
     | srt_preference
     | srt_readvertise
     | srt_reject
     | srt_resolve
     | srt_tag
  ;
  
  
negative.code:    RESOLVE
  ;
  
  srt_retain
  :
     RETAIN
  ;
  
  srt_tag
  :
     TAG tag = DEC
  