I am pretty sure the boundary=disputed tag is not documented anywhere, and it would be odd to suddenly make it a thing. The way forward should be first tagging it with something that gets rendered (b=administrative) plus some sort of disputed tag, and then going back on the wiki to workshop a way to describe this info.

@GerdP Apologies for this confusion. This rail is put on a ford on which people can walk on the two sides. I was a bit too lazy to draw three ways for that, so I merged these tags together.