xbox plots a box with a cross (x) in its top-right corner.
xbox(col = Seeblau, dim = c(1, 1), use_x = TRUE)The color to fill the box with (i.e., its background color).
Default: col = Seeblau.
The x- and y-dimensions of the box (as numeric). 
Default: dim = c(1, 1) (i.e., a unit square).
Plot a cross in upper right corner (as logical)? 
Default: use_x = TRUE.
The cross (x) appears rectangular when viewing the plot 
at the correct aspect ratio (as defined by dim).
post to add text to an xbox;   
slide to plot a new slide (or frame).
Other plot functions: 
slide(),
theme_grau(),
theme_unikn()
xbox()  # default box
 # Options:
xbox(col = Bordeaux)
# Options:
xbox(col = Bordeaux)
 xbox(dim = c(2, 1)) # 2:1 dimension (wider than high)
xbox(dim = c(2, 1)) # 2:1 dimension (wider than high)
