The element “h4” must not appear as a descendant of the “th” element.

The th element already carries semantic meaning as a table header cell. Nesting a heading element like h4 inside it creates a conflict in the document’s outline and semantic structure. Screen readers and other assistive technologies treat headings and table headers as distinct navigational landmarks, so combining them can confuse users who rely on these tools to understand page structure. A heading buried inside a table cell may break the expected heading hierarchy, making it harder for users to navigate by headings.

According to the HTML specification, the content model of th is “flow content, but with no header, footer, sectioning content, or heading content descendants.” This means h1, h2, h3, h4, h5, and h6 are all explicitly disallowed inside th.

The reason developers often place headings inside th is to achieve a specific visual style — larger, bolder text. But th elements are already rendered bold by default in most browsers, and any additional styling should be handled with CSS rather than repurposing heading elements.

How to Fix It

1. Remove the heading element from inside the th and use the text directly.
2. Style with CSS if you need the th content to look different from default styling.
3. Move the heading outside the table if it serves as a title or caption for the table. Consider using the <caption> element for table titles.

Examples

❌ Incorrect: Heading inside th

<table>
  <tr>
    <th><h4>Product</h4></th>
    <th><h4>Price</h4></th>
  </tr>
  <tr>
    <td>Widget</td>
    <td>$25</td>
  </tr>
</table>

This triggers the validation error because h4 elements are not allowed as descendants of th.

✅ Fixed: Plain text in th

<table>
  <tr>
    <th>Product</th>
    <th>Price</th>
  </tr>
  <tr>
    <td>Widget</td>
    <td>$25</td>
  </tr>
</table>

The simplest fix — just remove the heading tags. The th element already conveys that these cells are headers.

✅ Fixed: Using CSS for custom styling

If you need the header cells to have a specific visual appearance, use CSS:

<table>
  <tr>
    <th class="styled-header">Product</th>
    <th class="styled-header">Price</th>
  </tr>
  <tr>
    <td>Widget</td>
    <td>$25</td>
  </tr>
</table>

<style>
  .styled-header {
    font-size: 1.2em;
    text-transform: uppercase;
  }
</style>

✅ Fixed: Moving the heading outside and using caption

If the heading was meant to serve as a title for the table, use the <caption> element instead:

<table>
  <caption>Product Pricing</caption>
  <tr>
    <th>Product</th>
    <th>Price</th>
  </tr>
  <tr>
    <td>Widget</td>
    <td>$25</td>
  </tr>
</table>

The <caption> element is purpose-built for labeling tables and is well-supported by assistive technologies. You can also place a heading before the table if it fits your document’s heading hierarchy:

<h4>Product Pricing</h4>
<table>
  <tr>
    <th>Product</th>
    <th>Price</th>
  </tr>
  <tr>
    <td>Widget</td>
    <td>$25</td>
  </tr>
</table>

Both approaches keep your HTML valid while preserving clear semantics for both visual users and assistive technology.

Learn more:

MDN Reference

MDN - The Table Header element

→

MDN Reference

MDN - h1 to h6 - The HTML Section Heading elements

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