How do I add a group title to PGFPlotsX?


Suppose I have the code from the doc,

x = range(0; stop =2*pi, length = 100)
@pgf GroupPlot(
        group_style =
            group_size="2 by 1",
            xticklabels_at="edge bottom",
            yticklabels_at="edge left"
    PlotInc(Table(x, sin.(x))),
    PlotInc(Table(x, sin.(x .+ 0.5))),
    PlotInc(Table(x, cos.(x))),
    PlotInc(Table(x, cos.(x .+ 0.5))))

Which produces:


How do I add a group title on top of it, similar to how I could use “plot_title”?

Kind regards