The rows sat flush against their own heading and against the next directory, so an expanded node ran into
its neighbours as one undifferentiated column — the tree stopped reading as a hierarchy at exactly the
moment it had one.
pl-8 lines the rows up under the heading's TEXT rather than under its chevron, which is what makes "these
belong to that" legible without drawing a guide line, and py-2 separates the group from the headings above
and below it.