title: HTML Validator shows an error on a seemingly correct line of code
body: <p>I am creating a table for an university task. Every once in a while we have to put our code into a validator. For some reason the validator keeps showing these errors:
  <a href="https://i.ibb.co/dLnzTh2/error.png" rel="nofollow noreferrer">https://i.ibb.co/dLnzTh2/error.png</a>
  <br>
  The errors are about the <code>&lt;th&gt;</code> tag inside the <code>&lt;thead&gt;</code>.</p>
  <pre><code>&lt;table style=&quot;width: 700px&quot; &gt;
              &lt;thead&gt;
                  &lt;tr&gt;
                      &lt;th colspan=&quot;8&quot;&gt;Market Shares of Graphics Adapters in Q4 2013
                      &lt;/th&gt;
                  &lt;/tr&gt;
              &lt;/thead&gt;
              &lt;tbody&gt;
                  &lt;tr&gt;
                      &lt;td rowspan=&quot;2&quot;&gt;-&lt;/td&gt;
                      &lt;td rowspan=&quot;2&quot;&gt;Q4 2013&lt;/td&gt;
                      &lt;td rowspan=&quot;2&quot;&gt;Q3 2013&lt;/td&gt;
                      &lt;td colspan=&quot;4&quot; rowspan=&quot;1&quot; style=&quot;text-align: center&quot;&gt;Quarter over Quarter Changes&lt;/td&gt;
                      &lt;td rowspan=&quot;2&quot;&gt;2012&lt;/td&gt;
                  &lt;/tr&gt;
                  &lt;tr&gt;
                      &lt;td colspan=&quot;2&quot;&gt;Unit Shipments&lt;/td&gt;
                      &lt;td colspan=&quot;2&quot;&gt;Share&lt;/td&gt;
                  &lt;/tr&gt;
                  &lt;tr&gt;
                      &lt;td&gt;AMD&lt;/td&gt;
                      &lt;td&gt;18.30%&lt;/td&gt;
                      &lt;td&gt;20.70%&lt;/td&gt;
                      &lt;td colspan=&quot;2&quot;&gt;-10.40%&lt;/td&gt;
                      &lt;td colspan=&quot;2&quot;&gt;-2.40%&lt;/td&gt;
                      &lt;td&gt;19.70%&lt;/td&gt;
                  &lt;/tr&gt;
  &lt;/tbody&gt;
  &lt;/table&gt;
  </code></pre>
  <p>Any ideas what is causing this?
  For reference this is how the whole table looks like:
  <a href="https://i.ibb.co/LkMbWc9/table.png" rel="nofollow noreferrer">https://i.ibb.co/LkMbWc9/table.png</a></p>