Sortables: nested lists

Hi,
I'm looking at the nested list sortables.
Just a question about the example. It seems that I can't get an item
to be a subitem when there is no other subitem already.
# Drag us
# around
# and change
# Ipsum
# Lorem
# our
# positions
# Something else
# Foo bar
I can drag 'Ipsum' as a sub of 'positions' but bot as a sub of
'around'. How can this be achieved?