the position of the elements are specified with pos, which is either NULL, or a vector specifying the number of elements on a row, or a 2-columned matrix specifying the (x,y) position of each element.
when pos is NULL, the elements will be arranged on a circle; in this case, the number of elements to be positioned must be specified with N.
when pos is a vector, it specifies the number of elements in each row (if hor =TRUE) or in each column (if hor = FALSE).
For instance, with hor=TRUE and pos = c(3,2,1) the elements will be arranged in 3 rows (length of vector); on the top row 3 elements; on the second row 2; and on the third row 1 element will be positioned. All elements within a row are equally distributed horizontally; all rows are equally distributed vertically;
when pos is a matrix, it specifies the x(1st column) and y(2nd column) position of each element and is returned as such.
The offset from the x-axis and from the y-axis can be changed with mx and my.