Internal
Samples a point-level datum the way buildLineLayer does, so a binder layered on top of it can infer its own accessors from the same shape.
The extraction root (the SVG, or a panel element)
The binder config, read for selector and pointSelector
selector
pointSelector
One point's datum, or undefined when none can be reached
undefined
Samples a point-level datum the way buildLineLayer does, so a binder layered on top of it can infer its own accessors from the same shape.