Optionalcolor"#rrggbb" or "#rrggbbaa", overrides the role colour
Optionaldepth"ghost" draws as "test" until the ghost pass arrives
Optionalheadmm, default 0.3 x length; the thickness follows it (head radius 0.4 x headLength, shaft a third of that)
Unique within the overlay
OptionallabelOptionallabel"hover": the label only while the item or one of its qids is hovered; default "always"
OptionallengthOptionalqidsRelated model objects
OptionalroleOptionalsizeOptionalstoreyOptionaltooltipOptionalviews
A 3D arrow; lengths in mm. size "screen" keeps ~48 px on screen and ignores length