HTML Guide

A <li> element is used to define an item of a list, so adding the listitem role to it is redundant.

The ARIA listitem role can be used to identify an item inside a list of items. It is normally used in conjunction with the list role, which is used to identify a list container.

<section role="list">
  <div role="listitem">List item 1</div>
  <div role="listitem">List item 2</div>
  <div role="listitem">List item 3</div>
</section>

When possible, you should use the appropriate semantic HTML elements to mark up a list and its list items — <ul> or <ol>, and <li>. For example:

<ul>
  <li>List item 1</li>
  <li>List item 2</li>
  <li>List item 3</li>
</ul>

The issue you’re encountering comes from using the longdesc attribute on an iframe element. The longdesc attribute was historically used to provide a URL to a long description of the content. However, it is now considered obsolete and should not be used. Instead, you should use a regular a (anchor) element to provide a link to the description.

Here’s a short guide on how to fix this issue:

Original Code with longdesc

<iframe src="video.html" longdesc="description.html" title="Video"></iframe>

Updated Code with Regular a Element

The recommended approach is to use a regular a element to provide a link to the description, like in the following example:

<iframe src="video.html" title="Video"></iframe>

<p>
  <a href="description.html">Long description of the video content</a>
</p>

Explanation

• Original Code: The longdesc attribute is used on the iframe element, which is now obsolete.
• Updated Code: We remove the longdesc attribute and provide an external link using the a element to guide users to the description.

The deprecated property longdesc on img elements was used in HTML4 to specify the URL of a text or HTML file which contained a long-form description of the image. This could be used to provide optional added details beyond the short description provided in the title or alt attributes.

Here’s an example from HTML4:

<img
  src="cat.jpg"
  alt="Smiling Cat"
  longdesc="image-descriptions/smiling-cat.html" />

This, however, is no longer valid in HTML5 and can be converted to the following instead:

<a href="image-descriptions/smiling-cat.html">
  <img src="cat.jpg" alt="Smiling Cat" />
</a>

A main element cannot be nested within another main element.

The main element represents the primary content of a document or application, and there must be only one per page, not placed inside another main. The main element must not be used as a descendant of another main element. This is important for accessibility, semantic correctness, and helps screen readers correctly identify the main content region.

Invalid example (nested main):

<main>
  <h1>Welcome</h1>
  <main>
    <p>This nested main element is invalid.</p>
  </main>
</main>

Valid example (single main only):

<main>
  <h1>Welcome</h1>
  <section>
    <p>This section is valid and can be placed inside main.</p>
  </section>
</main>

If you need to divide the main content, use sectioning elements like section, article, or div inside a single main element, but never nest main inside main.

The main element represents the dominant contents of the document, so it should not be contained within another section.

A document must not have more than one main element that does not have the hidden attribute specified.

A hierarchically correct main element is one whose ancestor elements are limited to html, body, div, form without an accessible name, and autonomous custom elements. Each main element must be a hierarchically correct main element.

The main landmark role is used to indicate the primary content of a document. It can be added to an element by using role="main", but instead it’s preferable to just use the <main> element. In that case, it’s unnecessary to make the main role explicit. Examples:

<div role="main">
  <!-- this is a valid way to define a main role -->
</div>

<main>
   <!-- but this is shorter and uses correct semantic HTML  -->
</main>

In the days before HTML5, named anchors were used as a way to provide a link to a specific section of a document, for example:

<h2>
  <a name="section-5">Section 5</a>
</h2>

Now in HTML5, the name attribute is obsolete for <a> tags, and instead, you can use the id attribute of any element (not just <a>) as a way to navigate directly to it, for example:

<h2 id="section-5">Section 5</h2>

The warning regarding the use of the name attribute on the img element arises because the name attribute is considered obsolete in modern HTML. Historically, name was used to identify form controls and some other elements, but now it’s replaced by more standardized attributes like id.

To resolve this issue, replace the name attribute with the id attribute. The id attribute provides a unique identifier for the element within the document, which can be utilized for styling, scripting, or linking using fragment identifiers.

Here is an example of how to make this change:

HTML with obsolete name attribute:

<img src="example.jpg" name="myImage" alt="Descriptive text">

Updated HTML using the id attribute:

<img src="example.jpg" id="myImage" alt="Descriptive text">

In this modification:

• The name="myImage" is replaced with id="myImage".
• The remaining attributes like src and alt are retained for specifying the image source and providing alternative text, respectively.

The id attribute should be unique within the document, which ensures that JavaScript or CSS can target the element efficiently.

The <option> element no longer accepts a name attribute, which is now obsolete.

Example:

<select id="pet-select">
    <option value="">--Please choose an option--</option>
    <option value="dog">Dog</option>
    <option value="cat">Cat</option>
    <option value="hamster">Hamster</option>
</select>

The navigation landmark role is used to identify major groups of links used for navigating through a website or page content. It can be added to an element that contains navigation links by using role="navigation", but instead it’s preferable to just use the <nav> element. In that case, it’s unnecessary to make the navigation role explicit.

Examples:

<div role="navigation">
  <!-- this is a valid way to define a navigation role -->
</div>

<nav>
   <!-- but this is shorter and uses correct semantic HTML  -->
</nav>

The <meta> element no longer accepts a scheme attribute, it’s now obsolete and should be removed.

For example, old documents adhering to old definitions in DCMI (Dublin Core Metadata Initiative) use this HTML tag to define a date:

<meta name="DC.Date.Created" scheme="W3CDTF" content="2009-11-30" />

As the scheme attribute is now obsolete, it should now be removed. The following HTML code will pass current validations, but you should check the exact definition to use if you want to keep using the DCMI tags.

<meta name="DC.Date.Created" content="2009-11-30" />

The scope attribute must be used on a th element, not a td element.

The scope attribute helps define whether a header cell (th) refers to a column, row, or group of columns or rows in a table. According to current HTML standards, only th elements should use the scope attribute. Using scope on td elements is obsolete and invalidates your markup. To fix this, replace any td with scope with a th, and set the appropriate scope value (row, col, etc.).

Incorrect HTML Example (with validation error):

<table>
  <tr>
    <td scope="row">Monday</td>
    <td>Meeting</td>
  </tr>
</table>

Corrected HTML Example:

<table>
  <tr>
    <th scope="row">Monday</th>
    <td>Meeting</td>
  </tr>
</table>

Key points:

• Use scope="row" for row headers and scope="col" for column headers, but only on th elements.
• Never use the scope attribute on a td element.

Links created with the <a> element no longer accept a shape attribute. In order to define image maps, use the <area> element instead.

The sizes attribute is used to complement the srcset attribute on an <img> tag for responsive images, therefore it’s not valid if srcset is missing.

The W3C validator error you are seeing indicates that you’ve used the sizes attribute on an <img> element without providing a srcset attribute. According to HTML specifications, the sizes attribute is only meaningful when used alongside the srcset attribute.

The srcset attribute allows you to specify a list of possible image files for the browser to choose from based on conditions like the screen size or resolution. The sizes attribute helps the browser understand what size the image should be under specific conditions defined in srcset.

How to Fix the Issue

There are two options, adding or removing attributes.

1. Adding a srcset Attribute: If you need responsive images, make sure to include the srcset attribute in your <img> element.

2. Removing the sizes Attribute (if not necessary): If responsive images are not required and you’re not using srcset, simply remove the sizes attribute.

Example

Incorrect Markup:

<img src="image.jpg" sizes="(max-width: 600px) 480px, 800px" alt="Example Image">

Correct Markup with srcset:

<img src="image.jpg" 
     srcset="image-480w.jpg 480w, image-800w.jpg 800w" 
     sizes="(max-width: 600px) 480px, 800px" 
     alt="Example Image">

In this correct example, the srcset attribute provides two different images (image-480w.jpg and image-800w.jpg) and their corresponding widths (480w and 800w). The sizes attribute tells the browser to use the 480 pixels wide image if the viewport is 600 pixels or less, otherwise, it will use the full 800 pixels.

Correct Markup without sizes and srcset:

<img src="image.jpg" alt="Example Image">

If you don’t need responsive images, simply remove the sizes attribute to fix the issue.

Summary

Ensure that whenever you use the sizes attribute, you also include a srcset attribute. This makes sure that the browser can effectively make decisions about which image size to load in different scenarios.

To resolve the W3C Validator issue regarding the obsolete summary attribute on the table element, you should remove the summary attribute and instead provide a description of the table structure using a caption element.

Here’s how you can fix it:

• Remove the summary attribute: This attribute is no longer supported in modern HTML standards.
• Add a caption element: This element gives a brief description of the table, making it accessible and informing users what the table represents.

Example Before and After

Before Fixing (with obsolete summary attribute)

<table summary="This table shows the sales data for the year.">
    <tr>
        <th>Month</th>
        <th>Sales</th>
    </tr>
    <tr>
        <td>January</td>
        <td>$1000</td>
    </tr>
    <tr>
        <td>February</td>
        <td>$1200</td>
    </tr>
</table>

After Fixing (with caption element)

<table>
    <caption>Sales Data for the Year</caption>
    <tr>
        <th>Month</th>
        <th>Sales</th>
    </tr>
    <tr>
        <td>January</td>
        <td>$1000</td>
    </tr>
    <tr>
        <td>February</td>
        <td>$1200</td>
    </tr>
</table>

Additional Option: Using a figure Element

If you want to provide a more extensive description alongside your table, you can wrap the table in a figure element.

Example with figure

<figure>
    <figcaption>Sales Data for the Year</figcaption>
    <table>
        <tr>
            <th>Month</th>
            <th>Sales</th>
        </tr>
        <tr>
            <td>January</td>
            <td>$1000</td>
        </tr>
        <tr>
            <td>February</td>
            <td>$1200</td>
        </tr>
    </table>
</figure>

The <time> HTML element represents a specific period in time, which can be taken from the datetime attribute or from the text contents of the element.

In both cases, the time or datetime must be in a valid format, for example:

a valid year string

2011

a valid month string

2011-11

a valid date string

2011-11-18

a valid yearless date string

11-18

a valid week string

2011-W47

a valid time string

14:54

14:54:39

14:54:39.929

a valid local date and time string

2011-11-18T14:54:39.929

2011-11-18 14:54:39.929

a valid global date and time string

2011-11-18T14:54:39.929Z

2011-11-18T14:54:39.929-0400

2011-11-18T14:54:39.929-04:00

2011-11-18 14:54:39.929Z

2011-11-18 14:54:39.929-0400

2011-11-18 14:54:39.929-04:00

a valid duration string

PT4H18M3S

For example:

<p>
  The event will take place on <time datetime="2025-03-20T13:00">March 20, 2025</time>.
</p>

The textbox role, used to identify an element that allows the input of free-form text, is unnecessary for an <input> element of type text when it doesn’t have a list attribute.

The <tt> tag, used in HTML4 to apply a monospaced (fixed width) font to the text, was deprecated in HTML5. Instead, you should use CSS to apply the desired font.

Example, instead of this deprecated code:

<tt>This is deprecated</tt>

You can define a monospaced text using font-family:

<span style="font-family: monospace;">This is monospaced text</span>

The HTML <style> element contains style information for a document, or part of a document, defined in CSS. This element does not need the type attribute anymore, so it should be omitted.

For example, this style defines that <p> elements should be in red color.

<style type="text/css">
p {
  color: red;
}
</style>
<p>This text will be red.</p>

But, the type attribute is not used anymore, so we can just use this:

<style>
p {
  color: red;
}
</style>
<p>This text will be red.</p>

The default type for <script> tags is JavaScript, so you don’t need to include the type for JS resources.

<td> elements no longer accept a valign attribute. This can be achieved using CSS like this:

<td style="vertical-align:middle;">content</td>

Read about Normalization in HTML and CSS.

<label> tags are used to label inputs in form, which need to be present and visible in the document, for example:

<label for="age">Age</label>
<input id="age" />

In HTML5, there’s no need to specify the version attribute - it is now obsolete. Here’s an example minimal HTML document to start with:

<!DOCTYPE html>
<html lang="en">
  <head>
    <title>Test</title>
  </head>
  <body>
    <p></p>
  </body>
</html>