int i = textBox1.SelectionStart;
        var end = textBox1.Text.IndexOf(Environment.NewLine,i);
        var begin = textBox1.Text.XXX(Environment.NewLine,i); 
       /* the line above needs a method to find the firs occurance 
of newline before the i postion */
        bool isEmpty = textBox1.Text.Substring(begin,end-begin).Trim() == "";