/^
  (.)(?!\1)  # any character not followed by itself
  (.)(?!\1|\2)  # any character not followed by itself or previous
  (.)(?!\1|\2|\3)   # likewise unique...
  (.)(?!\1|\2|\3|\4)
  (.)
  \3 (?!\1|\2|\3|\4|\5) # 6th character must be same as 3rd
  (.)(?!\1|\2|\3|\4|\5|\6)  # 7th and 8th must be unique
   .
 $/x