[R] tcltk - automatically moving cursor to last line of tktext box - how?

[Søren Højsgaard]

Hi; I have a program which writes lines to a tktext box (of height, say, 10) with
      tkinsert(txto, "end", paste(so,"\n"))
I would like my program to be such that it automatically scrolls down through the text box when it is full so that I always see the last 10 lines written. Can anyone help on this?
Best regards
Søren