The selectors for a layer whose points are paired with these elements, or undefined when any point has no element -- a list that has slipped by one outlines the wrong mark for the rest of the layer, so the highlight is withdrawn instead.
One element per point, in point order
The selectors, or undefined
The selectors for a layer whose points are paired with these elements, or undefined when any point has no element -- a list that has slipped by one outlines the wrong mark for the rest of the layer, so the highlight is withdrawn instead.