I added Towpaths to the subsidaiaries page on my extension of the proposal. The problem is that as I said a sec ago, the path may be a footway, or just a phisical path, or even private. So it maybe subsidiary=left_private_towpath; right_highway_footway or something. Sometimes I think this just confusing to the extent that efficency may limit productivty. I guess this is why this area of mapping many elements of one bigger feature is rather achaic still.

Edit: note “name_left=” was the proposal for streenames left/right. So maybe it would be “subsidiary_left=”