Understanding "Persist to Workspace"

config.yml

   - persist_to_workspace:
          # Must be an absolute path, or relative path from working_directory. This is a directory on the container which is 
          # taken to be the root directory of the workspace.
          root: ~/app
          # “Paths” Must be relative path from root
          paths:
            - node_modules  # folder we want to keep for the next job
            - packages/my_project/build	# another folder