margin text

library(lattice)
library(grid)

leftText <- "words\nwords2\nwords3"
rightText <- "words\nwords2"
bottomPadding <- (max(sapply(gregexpr("\n", c(leftText, rightText)), length)) + 1L) * 2 + 2


xyplot(
  y ~ x, data.frame(x = rnorm(100), y = rnorm(100)),
  par.settings = list(layout.heights = list(bottom.padding = bottomPadding)),
  panel = function(x, y, ...) {
    panel.xyplot(x, y, ...)
    xscale <- current.viewport()$xscale
    yscale <- current.viewport()$yscale
    pushViewport(viewport(width = 2, height = 2, clip = TRUE))
    pushViewport(viewport(width = 0.5, height = 0.5, xscale = xscale, yscale = yscale))
    grid.text("v", unit(c(-0.5, 0, 0.5), "native"), unit(1, "npc") + unit(1, "mm"), c("center", "bottom"))
    grid.text(c("L", "U"), unit(0, "npc") - unit(2, "mm"), unit(c(-2, 2), "native"), c("center", "bottom"),
              gp = gpar(col = "red"))
    popViewport(2)
  },
  page = function(page){
    grid.text(leftText, 0.02, 0.02, c("left", "bottom"))
    grid.text(rightText, 0.98, 0.02, c("right", "bottom"))
  }, scales = list(tck = c(1, 0))
)