Enumeration members
Area
Area: = "area"
Bar
Bar: = "bar"
Circle
Circle: = "circle"
GanttBar
GanttBar: = "gantt-bar"
Line
Line: = "line"
Map
Map: = "map"
Pie
Pie: = "pie"
Polygon
Polygon: = "polygon"
Shape
Shape: = "shape"
Square
Square: = "square"
Text
Text: = "text"
Type of mark for a given marks card in a viz.