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

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

step:./plan.py
               state = SUCCEEDED
                need = PLAN
           using_env = STEPUP_PATH_FILTER [dynamic]
             creator   root:
              source   file:plan.py
             product   file:www/plan.py
             product   step:./plan.py  # wd=www

file:www/plan.py
               state = CONFIRMED
             creator   step:./plan.py
                sink   step:./plan.py  # wd=www

step:./plan.py  # wd=www
               state = SUCCEEDED
                need = PLAN
           using_env = PUBLIC [dynamic]
                     = STEPUP_PATH_FILTER [dynamic]
             creator   step:./plan.py
              source   file:www/plan.py
             product   file:www/index.md
             product   step:cp -p index.md ../../public/www/index.md  # wd=www

file:www/index.md
               state = CONFIRMED
             creator   step:./plan.py  # wd=www
                sink   step:cp -p index.md ../../public/www/index.md  # wd=www

step:cp -p index.md ../../public/www/index.md  # wd=www
               state = SUCCEEDED
                need = DEFAULT
             creator   step:./plan.py  # wd=www
              source   file:www/index.md
             product   file:../public/www/index.md
                sink   file:../public/www/index.md

file:../public/www/index.md
               state = BUILT
             creator   step:cp -p index.md ../../public/www/index.md  # wd=www
              source   step:cp -p index.md ../../public/www/index.md  # wd=www
