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.
expand_plot(
expand_x = expand_scale(c(0.1, 0.1)),
expand_y = expand_scale(c(0.1, 0.1))
)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 expand_scale() to
generate the values for the expand argument.