anchor.diff:    BOOT
     (
       boot_kickstart
  +    | boot_null
       | boot_nxos
       | boot_system
     )
  
positive.code: boot_kickstart
  :
    KICKSTART image = WORD (SUP_1 | SUP_2)? NEWLINE
  ;
  
  boot_nxos
  
negative.code: s_null
  :
    (
      CLI
      | CLOCK
      | ERRDISABLE
      | FEATURE
  