edge { arrow-style: none; }

# the arrow is not drawn
[ Mainau ] --> [ Unteruhlingen ] { border-style: dotted; }
# there is no arrow, so the style is ignored
[ Mainau ] -- { arrow-style: closed; } [ Unteruhlingen ]

# these override the class default:
[ Oberuhlingen ] <--> { arrow-style: closed; } [ Unteruhlingen ]
[ Uhlingen ] <--> { arrow-style: filled; } [ Oberuhlingen ]

# arrows are again not rendered
[ Hagnau ] { flow: down; } <--> [ Uhlingen ]
[ Hagnau ] <--> [ Oberuhlingen ]

