Neither the end node nor the start node have a visible label. I suspect this is intentional but they shouldn't take a label argument then.

The label seems to serve as a reference. If have `-> [<end>a]` and `-> [<end>b]` then that's different than having two instances of `-> [<end>a]` from different source nodes.

Being able to visibly label them would still make a lot of sense.