Add line style to legend

Specific Domains Visualization
1

Is there a way to add something (in this case a line style) to a legend without plotting it? I am using Plot.jl

MWE

aa = 1:10
bb = 10 .* rand(10)
cc = 10 .* rand(10)
dd = 10 .* rand(10)
ee = 10 .* rand(10)
ff = 10 .* rand(10)
gg = 10 .* rand(10)

plot(aa, bb,color=1,label = "Cl 1")
plot!(aa,cc,color=1,ls=:dashdot,label = false)
plot!(aa,dd,color=2,label = "Cl 2")
plot!(aa,ee,color=2,ls=:dashdot,label = false)
plot!(aa,ff,color=3,label = "Cl 3")
plot!(aa,gg,color=3,ls=:dashdot,label = false)
plot!(colour = :black, label = "High") #this does nothing
plot!(colour = :black, ls=:dashdot, label = "Low")  #this does nothing
2

I worked around it by first plotting black lines and then the rest of the plot on top of it. This results in some lines being darker than in the legend, but it works for now.

plot(aa, bb,colour = :black, label = "High")
plot!(aa,cc,colour = :black, ls=:dashdot, label = "Low")
plot!(aa, bb,color=1,label = "Cl 1")
plot!(aa,cc,color=1,ls=:dashdot,label = false)
plot!(aa,dd,color=2,label = "Cl 2")
plot!(aa,ee,color=2,ls=:dashdot,label = false)
plot!(aa,ff,color=3,label = "Cl 3")
plot!(aa,gg,color=3,ls=:dashdot,label = false)

image

3

you could use alpha=0.0, or plot outside of the plot boundaries (use xlims, ylims)

4

The problem with alpha = 0.0 is that the legend disappears though (as it uses the same transparency). I think plotting outside the area and fixing the lims or alternatively plotting a single point as a line - plot!([0], [0]) - is the way to go