HTML Checking for Large Sites

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 button element, or an element with the role=button attribute, is not allowed to be nested inside an <a> element.

An <a> element cannot contain a descendant element with the attribute tabindex.

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

The href attribute of an <a> element contains an invalid character, that should be properly encoded as a URI percent-encoded character.

The target attribute on <a> elements can’t be blank.

This attribute defines the browsing context for links, that is, where should the linked documents be opened. This was used extensively on the now deprecated <frame> element, so you could give the name of the frame to open the document in, but is now more used to force links to open in a separate tab or window using target="_blank". Another option is using a name, so the new browsing context can be referred to on subsequent clicks on links with the same target.

For example, this will force the links to open on a new tab:

<a href="https://example.com" target="_blank">will open a blank tab</a>

The href attribute on an a tag expects a valid URL, but only http:// was found.

<a> tags can be used to link to an email address using the mailto protocol in the href attribute. Ensure that there is no space in the email address.

<a href="mailto: liza@example.com">This is wrong as it contains an space</a>

<a href="mailto:liza@example.com">This is OK</a>

Hash (#) characters can be used in an href attribute to link to a specific part of a document.

For example, if we have this page with several sections, each of them marked with an ID:

<h1>Frequently Asked Questions</h1>

<h2 id="pricing">Pricing</h2>
<p>All about pricing...</p>

<h2 id="terms">Terms</h2>
<p>You can find our terms at...</p>

<h2 id="guarantee">Guarantee</h2>
<p>We offer a guarantee...</p>

You can link to a specific part of that document, for example if this page URL is /faqs and you want to link to the Guarantee section you could use:

<a href="/faqs#guarantee">Guarantee</a>

Or, if you’re linking from inside the same document, for example in a table of contents, you could just use:

<a href="#guarantee">Guarantee</a>

As there can only be one fragment in an URL, the # character should only be used once. The following would be an invalid href:

<a href="/faqs#guarantee#pricing">Bad</a>

If needed, the # could be encoded as %23.