Draw a line of the specified width onto the graph. I<width> can be a
floating point number. If the color is not specified, the drawing is done
'invisibly'. This is useful when stacking something else on top of this
line. Also optional is the legend box and string which will be printed in
Draw a line of the specified width onto the graph. I<width> can be a
floating point number. If the color is not specified, the drawing is done
'invisibly'. This is useful when stacking something else on top of this
line. Also optional is the legend box and string which will be printed in