y">(empty)</span>
      <span id="unmergeable">(unmergeable)</span>

      <tr-v-ui-scalar-span id="scalar" on-click="openHistogram_"></tr-v-ui-scalar-span>

      <span id="open_histogram" on-click="openHistogram_">
        <svg viewbox="0 0 128 128">
          <rect x="16" y="24" width="32" height="16"/>
          <rect x="16" y="56" width="96" height="16"/>
          <rect x="16" y="88" width="64" height="16"/>
        </svg>
      </span>

      <span id="histogram"></span>

      <span id="close_histog