“th” start tag in table body.

When you write a <table> without explicitly using <thead> and <tbody>, the HTML parser automatically wraps your <tr> elements in an implicit <tbody>. If any of those rows contain <th> elements intended as column headers, the validator flags them because <th> cells in <tbody> are unexpected — the parser sees header cells appearing in what should be the data body of the table.

While <th> elements are technically valid inside <tbody> (for example, as row headers), this warning usually indicates a structural problem: your column headers aren’t properly separated from your data rows. Properly structuring your table with <thead> and <tbody> matters for several reasons:

• Accessibility: Screen readers use table structure to help users navigate. A <thead> section clearly identifies column headers, making it easier for assistive technology to announce what each data cell represents.
• Styling and behavior: CSS selectors like thead th and tbody td let you target headers and data cells independently. Browsers can also use <thead> and <tbody> to enable scrollable table bodies while keeping headers fixed.
• Standards compliance: Explicitly defining table sections removes ambiguity and ensures consistent parsing across all browsers.

To fix this issue, wrap the row containing your <th> column headers in a <thead> element, and wrap your data rows in a <tbody> element.

Examples

❌ Incorrect: <th> in implicit table body

Here, the parser wraps all rows in an implicit <tbody>, so the <th> elements end up inside the table body:

<table>
  <tr>
    <th>Name</th>
    <th>Age</th>
  </tr>
  <tr>
    <td>Liza</td>
    <td>49</td>
  </tr>
  <tr>
    <td>Joe</td>
    <td>47</td>
  </tr>
</table>

✅ Correct: <th> in explicit <thead>

Wrapping the header row in <thead> and data rows in <tbody> resolves the issue:

<table>
  <thead>
    <tr>
      <th>Name</th>
      <th>Age</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>Liza</td>
      <td>49</td>
    </tr>
    <tr>
      <td>Joe</td>
      <td>47</td>
    </tr>
  </tbody>
</table>

✅ Correct: <th> as row headers inside <tbody>

If you intentionally use <th> elements inside <tbody> as row headers, add the scope attribute to clarify their purpose. This is valid and won’t trigger the warning when the table also has a proper <thead>:

<table>
  <thead>
    <tr>
      <th scope="col">Name</th>
      <th scope="col">Age</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <th scope="row">Liza</th>
      <td>49</td>
    </tr>
    <tr>
      <th scope="row">Joe</th>
      <td>47</td>
    </tr>
  </tbody>
</table>

The scope="row" attribute tells assistive technology that these <th> cells are headers for their respective rows, while scope="col" identifies column headers. This combination provides the best accessibility for table data.

Learn more:

MDN Reference

MDN: The Table Header element

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WHATWG Spec

HTML Spec: the th element

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