margin(t = 0, r = 0, b = 0, l = 0, unit = "pt")
This is a convenience function that creates a grid unit object of the correct length to use for setting margins.
margin(4)[1] 4pt 0pt 0pt 0ptmargin(4, 2)[1] 4pt 2pt 0pt 0ptmargin(4, 3, 2, 1)[1] 4pt 3pt 2pt 1pt