there's no wiki definitions yet and it seems that they have overlapping entries.
the guard_rail entries predominantly have "thicker fences" that are commonly found near cliffs and dangerously prone places at roadside. if this the right definition, i can clean the entries up.
however, the rail and railing seem to be no different at all. is this the one with "thinner fences" in pedestrian walkways/overpass like post #60649 and post #367314? inside the building like post #882695? how about a "thicker" rail but located in buildings like terraces like post #892579? if these two are the same i propose a tag alias: rail -> railing or whichever is appropriate.
hoping for your guidance. thanks.
EDIT: changed thread title from wiki definitions: guard_rail, rail, railing to Tag Alias: rail -> railing
Updated