Styling multilevel FactorRange axis

Is there currently any way to style multi-level categorical axes? E.g. I would like to modify the grey vertical bars between the different categories, see Screen Shot 2019-07-10 at 4.59.12 PM.png

Turns out I was looking in the wrong place (plot.x_range). The actual properties are called plot.xaxis[0].separator_line_*

FYI can typically omit the subscript, as a convenience these lists are “splattable”, e.g

plot.xaxis.separator_line_width = 2