Group of another graphs. Legend sample will be combined from samples of nested graphs.
<= Plan $mol_plot_group
series_x <= plan_x /
series_y <= plan_y /
graphs /
<= Plan_line $mol_plot_line
<= Plan_dots $mol_plot_dot
See $mol_plot_graph.
graphs() : $mol_plot_graph[]
List of graphs. series_x, series_y will be injected to every of them.