his is an advance technique. You probably need to
                    understand how to build a
                    <a href="line_basic.html">basic line plot</a> first, and
                    then a
                    <a href="line_several_group.html"
                      >lineplot with several groups</a
                    >.
                  </li>
                  <br />
                  <li>
                    Instead of building one main svg area as usual,
                    <u>many svg areas</u