In addition to geometric element layers (geoms) based on
base-ggplot2 layers like geom_point() but specified to matrix factors
as geom_row_point(), ordr introduces ggproto
classes for some additional geometric elements commonly used in biplots.
The factor-specific geoms invoke the statistical transformation layers
(stats) stat_rows() and stat_cols(), which specify the matrix factor.
Because each ggplot layer consists of only one stat and one geom, this
necessitates that ggproto classes for new stats must also come in *Rows
and *Cols flavors.
ggplot2::ggplot2-ggproto and ggplot2::ggproto for explanations
of base ggproto classes in ggplot2 and how to create new ones.