[category axis id]; the axis is laid out by the group.
The category axis's line, in px; null for none.
Every bar, in px.
By point, its category's label left of the axis; null where the axis shows none.
The gap between bars as a percentage of a bar's height.
The plot's inside, in px: the bars' room right of the axis.
A funnel: a bar per point, the first at the top, each as wide as its value's share of the largest and centered on the plot, beside a category axis the group draws itself.