[Tagging] Service=* used for highways and railways

[Steve Bennett]

For some reason it completely escaped me that service=* is supposed to
be used for both railways (eg, service=spur) and roads
(service=alley). I don't really want to debate this situation with a
view to changing it, but could someone give me a quick explanation on
how this arose? It seems a little odd, and somewhat confusing, to me.

Steve