root:
             product   file:plan.py
             product   step:./plan.py

file:plan.py
               state = CONFIRMED
             creator   root:
                sink   step:./plan.py

step:./plan.py
               state = FAILED
                need = PLAN
           using_env = STEPUP_PATH_FILTER [dynamic]
             creator   root:
              source   file:plan.py

(step:touch vol.txt)
               state = PENDING
                need = DEFAULT
             product   (file:vol.txt)
                sink   (file:vol.txt)

(file:vol.txt)
               state = VOLATILE
             creator   (step:touch vol.txt)
              source   (step:touch vol.txt)
