The element “table” must not appear as a descendant of the “caption” element.

The <caption> element is designed to be a brief, descriptive label for its parent <table>. According to the HTML specification, <caption> accepts flow content but explicitly forbids descendant <table> elements. This restriction exists because a table nested inside a caption creates a confusing and semantically meaningless structure — the caption is supposed to describe the table, not contain another one.

Why this is a problem

• Accessibility: Screen readers announce the <caption> as the title of the table. A nested table inside a caption creates a confusing experience for assistive technology users, as the relationship between the tables becomes ambiguous and the caption loses its descriptive purpose.
• Standards compliance: The WHATWG HTML living standard explicitly states that <caption> must have “no <table> element descendants.” Violating this produces a validation error.
• Rendering inconsistencies: Browsers may handle this invalid nesting differently, leading to broken or unpredictable layouts across different environments.

How to fix it

1. Remove the table from the caption. The <caption> should contain only text and simple inline elements like <span>, <strong>, <em>, or <a>.
2. Place the nested table outside the parent table, either before or after it, or restructure your layout so both tables are siblings.
3. If the data in the nested table is genuinely related to the caption’s purpose, consider expressing it as plain text or using a different structural approach entirely.

Examples

❌ Incorrect: A table nested inside a caption

<table>
  <caption>
    Summary
    <table>
      <tr>
        <td>Extra info</td>
        <td>Details</td>
      </tr>
    </table>
  </caption>
  <tr>
    <th>Name</th>
    <th>Score</th>
  </tr>
  <tr>
    <td>Alice</td>
    <td>95</td>
  </tr>
</table>

This triggers the validation error because a <table> appears as a descendant of the <caption> element.

✅ Correct: Caption contains only text, tables are separate

<table>
  <caption>Summary — Extra info: Details</caption>
  <tr>
    <th>Name</th>
    <th>Score</th>
  </tr>
  <tr>
    <td>Alice</td>
    <td>95</td>
  </tr>
</table>

If the extra information truly requires its own table, place it as a sibling:

<table>
  <caption>Summary</caption>
  <tr>
    <th>Name</th>
    <th>Score</th>
  </tr>
  <tr>
    <td>Alice</td>
    <td>95</td>
  </tr>
</table>

<table>
  <caption>Additional details</caption>
  <tr>
    <td>Extra info</td>
    <td>Details</td>
  </tr>
</table>

✅ Correct: Caption with inline formatting only

<table>
  <caption>
    <strong>Quarterly Results</strong> — <em>All figures in USD</em>
  </caption>
  <tr>
    <th>Quarter</th>
    <th>Revenue</th>
  </tr>
  <tr>
    <td>Q1</td>
    <td>$1.2M</td>
  </tr>
</table>

This is valid because the <caption> contains only text and inline elements (<strong>, <em>), with no <table> descendants.

Learn more:

MDN Reference

HTML table element

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MDN Reference

HTML caption element

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WHATWG Spec

HTML tables

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