The xside and yside variants of geoms are plotted
along the x-axis and y-axis respectively of their main panel's data mapping.
The positional scale here is shared between the main panel and the side
panel. The related positional scale type of the side panel, i.e. the y axis
of the xside panel (xsidey) or the x axis of the yside panel (ysidex), is
determened automatically by ggplot2 default scales. However, you can
override this by using the continuous or
discrete variants within ggside. This
allows the user to select the scale type or transform most approprate for
their side panels.