HTML Guide

Table rows on the same <table> element must have the same number of columns, which comes determined by the first tr row.

For example, this table is wrong as the first row defines 2 columns, while the second row tries to use 4 columns:

<table>
    <tr>
      <td>Liza</td>
    </tr>

    <tr>
      <td>Jimmy</td>
      <td>14</td>
    </tr>
</table>

A <table> contains a <tr> row that has less <td> columns than the column count established by the first row. Check the table to ensure all rows have the same number of columns.

For example, in the following table, the first <tr> row defines that it’s 2 columns wide, but the second <tr> row tries to use only 1 column:

<table>
  <!-- This first row sets the table as 2 columns wide -->
  <tr>
    <td>First</td>
    <td>Second</td>
  </tr>

  <!-- This second row has only 1 column -->
  <tr>
    <td>Wrong</td>
  </tr>
</table>

A <table> contains an incoherent number of columns on one of its rows. Check the structure of the table to find the invalid row.

For example, in the following table, the first <tr> row defines that it’s 2 columns wide, but the second <tr> row tries to use 5 columns by means of a colspan attribute:

<table>
  <!-- This first row sets the table as 2 columns wide -->
  <tr>
    <td>First</td>
    <td>Second</td>
  </tr>

  <!-- This second row tries to use 5 columns -->
  <tr>
    <td colspan="5">Wrong</td>
  </tr>
</table>

The <th> HTML element defines a cell as a header of a group of table cells, and must appear within a <tr> element.

In the following example for a simple table, the first <tr> contains two <th> header cells naming the values for each column:

<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>

The <table> element does not accept a height attribute. Use CSS instead.

A table row tr has been found, containing no td cells. Check the table and remove empty rows.

Table contents is organized in rows using the <tr> element, which must contain cells using the <td> element, as in this example:

<table>
  <thead>
    <tr>
      <th>Name</th>
      <th>Age</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>Liza</td>
      <td>12</td>
    </tr>
    <tr>
      <td>Jimmy</td>
      <td>14</td>
    </tr>
  </tbody>
</table>

A tr with no td cells on it will raise an issue, as in this example:

<table>
  <thead>
    <tr>
      <th>Name</th>
      <th>Age</th>
    </tr>
  </thead>
  <tbody>
    <tr>

    </tr>
    <tr>
      <td>Jimmy</td>
      <td>14</td>
    </tr>
  </tbody>
</table>

Note that self-closing <tr/> elements also count as empty rows as are like <tr></tr>.

An <a> element has been found in an invalid place within a <table> element.

For example, the following code would cause this issue:

<table>
  <tr>
    <a href="#">link</a>
  </tr>
</table>

Instead, the <a> element should be inside a <td> element, as a <tr> can’t hold content directly:

<table>
  <tr>
    <td>
      <a href="#">link</a>
    </td>
  </tr>
</table>

To fix the W3C HTML Validator issue stating that a heading element like h1, h2, h3, h4, h5 or h6 must not appear as a descendant of the th element, you need to ensure that the HTML structure follows the specifications where a heading element (h1 to h6) is not placed within a table cell element like th.

Here’s an example of what might be causing the issue and how you can correct it:

Incorrect HTML:

<table>
  <tr>
    <th>Month</th>
    <th><h1>Revenue</h1></th> <!-- Incorrect placement of h1 inside th -->
  </tr>
  <tr>
    <td>January</td>
    <td>$500</td>
  </tr>
</table>

Corrected HTML:

<h1>Revenue per month</h1>
<table>
  <tr>
    <th>Month</th>
    <th>Revenue</th>
  </tr>
  <tr>
    <td>January</td>
    <td>$500</td>
  </tr>
</table>

In the corrected example, the issue is fixed by removing the h1 element from the th element. If you need to style the text inside the th element differently, you can achieve that via CSS without nesting heading elements inside table cell elements.

To fix the W3C HTML Validator issue stating that a heading element like h1, h2, h3, h4, h5 or h6 must not appear as a descendant of the th element, you need to ensure that the HTML structure follows the specifications where a heading element (h1 to h6) is not placed within a table cell element like th.

Here’s an example of what might be causing the issue and how you can correct it:

Incorrect HTML:

<table>
  <tr>
    <th>Month</th>
    <th><h2>Revenue</h2></th> <!-- Incorrect placement of h2 inside th -->
  </tr>
  <tr>
    <td>January</td>
    <td>$500</td>
  </tr>
</table>

Corrected HTML:

<h2>Revenue per month</h2>
<table>
  <tr>
    <th>Month</th>
    <th>Revenue</th>
  </tr>
  <tr>
    <td>January</td>
    <td>$500</td>
  </tr>
</table>

In the corrected example, the issue is fixed by removing the h2 element from the th element. If you need to style the text inside the th element differently, you can achieve that via CSS without nesting heading elements inside table cell elements.

To fix the W3C HTML Validator issue stating that a heading element like h1, h2, h3, h4, h5 or h6 must not appear as a descendant of the th element, you need to ensure that the HTML structure follows the specifications where a heading element (h1 to h6) is not placed within a table cell element like th.

Here’s an example of what might be causing the issue and how you can correct it:

Incorrect HTML:

<table>
  <tr>
    <th>Month</th>
    <th><h3>Revenue</h3></th> <!-- Incorrect placement of h3 inside th -->
  </tr>
  <tr>
    <td>January</td>
    <td>$500</td>
  </tr>
</table>

Corrected HTML:

<h4>Revenue per month</h4>
<table>
  <tr>
    <th>Month</th>
    <th>Revenue</th>
  </tr>
  <tr>
    <td>January</td>
    <td>$500</td>
  </tr>
</table>

In the corrected example, the issue is fixed by removing the h3 element from the th element. If you need to style the text inside the th element differently, you can achieve that via CSS without nesting heading elements inside table cell elements.