Add reference lines to plot in VegaLite.jl

Specific Domains Visualization
3

Just did this:

df |> @vlplot(x=:m, height=400, width=400) +
    @vlplot(mark={:point, filled=true, color=:blue}, y=:ul) +
    @vlplot(mark={:point, filled=true, color=:blue}, y=:ll) +
    @vlplot(mark={:line, color=:red}, y={datum=26}, x={[i for i in 0.0:0.1:5], title="M"}) +
    @vlplot(mark={:line, color=:black}, y={datum=0}, x={[i for i in 0.0:0.1:5], title="M"}) +
    @vlplot(mark={:rule, color=:blue}, y=:ul, y2=:ll)