Hi Alex, thx for your time to comment. When using "use_sidepath" or "separate" wiki states that there should be drawn a compulsory line (eg footpath/sidewalk) to really redirect routing over this sidepath. Since this line is not avaliable (only a small part) the edit was meanigfull and helping automated routing tools ro route by foot over the Leinestrasse. There is only 1 usage of foot=optional_sidepath tagged in the world of osm, this could be a clou that it is a rather odd tagging scheme. Of course it is not wrong to introduce new tags. Happy mapping, kind regards, Joris