if every row defined by <code>:elementName</code> has the same value for a column <code>:columnElementName</code>.</p>
<p><code>:elementName</code> must be an array of elements</p>
<p><code>:columnElementName</code> must be an element, for example:</p>
<pre><code class="hljs css language-html"><span class="hljs-tag">&lt;<span class="hljs-name">table</span>&gt;</span>
  <span class="hljs-tag">&lt;<span class="hljs-name">tr</span>&gt;</span>
    <span class="hljs-tag">&lt;<span class="hljs-name">td</span>&gt;