public override string ToString ()
{
return string.Format ("{0},{1},{2},{3}", Double.IsNaN (left) ? "Auto" : left.ToString (),
Double.IsNaN (top) ? "Auto" : top.ToString (),
Double.IsNaN (right) ? "Auto" : right.ToString (),
Double.IsNaN (bottom) ? "Auto" : bottom.ToString ());
}