expand_plot()
is a convenience function that expands the scales of a
ggplot, as the large node sizes in a DAG will often get clipped in themes
that don't have DAGs in mind.
Vector of range expansion constants used to add some
padding around the data, to ensure that they are placed some distance away
from the axes. Use the convenience function ggplot2::expansion()
to
generate the values for the expand argument.