writelabel.Rdadds one-character label on left-upper margin, next to a plot
writelabel(text = NULL, nr = 1, at = -0.1, line = 1, cex = 1.5, ...)text to write.
integer; if text = NULL: nr is converted to uppercase letter.
relative distance of label position, from left margin of plot region.
line above the plot region of label position.
relative size of label.
arguments passed to R-function mtext.