event log

> 0   (sequence (capture "a") "b" (capture (backmatch)))
> 1   (capture "a")
> 2   "a"
  2 > "a"
  1 > (capture "a")
> 3   "b"
  3 > "b"
> 4   (capture (backmatch))
> 5   (backmatch)
  5 > (backmatch)
  4 > (capture (backmatch))
  0 > (sequence (capture "a") "b" (capture (backmatch)))