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