code: func (txt *Text) WriteRune(r rune) (n int, err error) {
  	var b [4]byte
  	n = utf8.EncodeRune(b[:], r)
  	txt.buf = append(txt.buf, b[:n]...)
  	txt.drawBuf()
  	return n, nil
  }
docs: // WriteRune writes a rune to the Text. This method never fails, always returns utf8.RuneLen(r), nil.