      and `columns`, skipping the 2nd `relpos`, because the containing
              block of the spanner is the multicol container.
              https://drafts.csswg.org/css-multicol/#column-span
            -->
            <div class="anchor1"></div>
            <!--
              The containing block of this target is inside a spanner.
            -->
            <div class="target"
                 data-offset-x=10 data-offset-y=0
                 data-expected-width=40 data-expected-height=20></div>
 