Start tag for “table” seen but the previous “table” is still open.

A table can only hold another table inside one of its cells, so a <table> start tag placed directly inside an open table, outside any <td> or <th>, is an error.

Between <table> and </table>, HTML allows only table parts: <caption>, <colgroup>, <thead>, <tbody>, <tfoot> and <tr>. Content, a nested table included, goes in a <td> or <th> cell. When the parser meets a new <table> tag anywhere else in an open table, it closes the open table at that point and starts the new one after it. The two tables end up as siblings in the DOM, and the </table> written for the outer table has nothing left to close, so the validator also reports a stray end tag.

Two mistakes usually cause this. One is a missing </table>: a table never gets closed, and the next table on the page starts inside it. The other is a wrapper table with another table directly inside it and no <tr> or <td> in between, such as one left behind by a WYSIWYG editor.

Close the first table before the next one starts, or remove the extra wrapper. If you do want one table inside another, put the inner table in a <td> of the outer one. To center a table or add space around it, use CSS on the table itself instead of wrapping it in another table.

Invalid example

<table>
  <table>
    <tr>
      <th>Day</th>
      <th>Opening hours</th>
    </tr>
    <tr>
      <td>Monday</td>
      <td>9:00 to 17:00</td>
    </tr>
  </table>
</table>

Valid example

<table>
  <tr>
    <th>Day</th>
    <th>Opening hours</th>
  </tr>
  <tr>
    <td>Monday</td>
    <td>9:00 to 17:00</td>
  </tr>
</table>

Learn more:

MDN Reference

MDN Web Docs: <table>

→

WHATWG Spec

HTML Standard: Tabular data

→