HTML Guide

When an img element has an empty alt attribute, its role is implicitly decorative, so it must not specify a role attribute.

The dialog element does not require or permit a role="dialog" attribute according to HTML standards.

The <dialog> element has an implicit ARIA role of dialog, so adding role="dialog" is redundant and not valid per the specification. Instead, simply use the <dialog> element without an explicit role attribute.

Details:

According to the WHATWG HTML standard and ARIA specification, native <dialog> elements automatically have the correct role. Adding role="dialog" can cause HTML validation errors, as the validator interprets this as a misuse or redundancy.

Correct usage:

<dialog>
  <p>This is a dialog box.</p>
  <button>Close</button>
</dialog>

Incorrect usage (causes validation error):

<dialog role="dialog">
  <p>This is a dialog box.</p>
  <button>Close</button>
</dialog>

Removing the role="dialog" attribute resolves the W3C validation issue while maintaining accessibility.

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

srcset contains candidates without a width descriptor while sizes is present, so each candidate must use a width (w) descriptor.

When an img has sizes, every srcset candidate must include a width descriptor like 320w, not a pixel density descriptor like 1x. Mixed descriptors are not allowed in the same srcset. Use either:

• Width descriptors with sizes (e.g., 320w, 640w, 1024w)
• Density descriptors without sizes (e.g., 1x, 2x)

The browser uses sizes to map CSS layout width to the best w candidate. Without sizes, density (x) can be used, but not together with sizes.

HTML examples

Reproduce the issue (invalid: sizes + x descriptors)

<img
  src="photo-640.jpg"
  srcset="photo-640.jpg 1x, photo-1280.jpg 2x"
  sizes="(max-width: 600px) 100vw, 600px"
  alt="Sample photo">

Fix using width descriptors with sizes (valid)

<img
  src="photo-640.jpg"
  srcset="photo-320.jpg 320w, photo-640.jpg 640w, photo-1280.jpg 1280w"
  sizes="(max-width: 600px) 100vw, 600px"
  alt="Sample photo">

Alternative fix: remove sizes and use density descriptors (valid)

<img
  src="photo-640.jpg"
  srcset="photo-640.jpg 1x, photo-1280.jpg 2x"
  alt="Sample photo">

The icon value for attribute role is not a valid ARIA role.

ARIA Roles: Overview

ARIA roles are used to enhance accessibility by clearly defining the role and purpose of an element for assistive technologies. However, there are defined roles that you need to adhere to:

• Standard roles include button, checkbox, alert, dialog, img, etc.
• There is no ARIA role named icon.

Solution

To fix the issue, you need to use a valid ARIA role that accurately describes the purpose of the span element. If your intention is to convey that the span contains an icon, you might want to reconsider whether you need a role at all. Often, purely decorative elements should not have a role, or you might use an img role if it conveys a meaningful image.

Here’s how you can address this:

1. No ARIA role (if purely decorative): If the icon is purely decorative and does not add meaningful content to your page, you should remove the role attribute entirely.

   <span class="icon"></span>

2. Using img role (if it represents an image): If the span represents an image or an icon that conveys meaningful information, you can use role="img" and provide a proper aria-label.

   <span class="icon" role="img" aria-label="Icon Description"></span>

3. Using an appropriate role (if interactive): If the icon is part of an interactive element, you might need a different role. For instance, if the icon is inside a button:

   <button>
      <span class="icon" aria-hidden="true"></span>
      Button text
   </button>

   Here, aria-hidden="true" is used to hide the decorative icon from screen readers as the text provides the necessary context.

The role attribute value navigation is invalid for a ul element, as it should be used with a nav element or similar suitable elements.

In HTML, the role attribute defines what an element represents in the context of accessible web technologies, primarily for assistive tools like screen readers. The nav element represents a section of a page intended for navigational links, and it inherently provides the role of navigation. If you want to make a ul element serve as navigation, it is more appropriate to use it inside a nav element, or alternatively, set a valid ARIA role on the element itself.

Detailed Explanation

HTML5 introduced a specific set of elements with implicit ARIA roles and behaviors, like the nav element, which implicitly has the navigation role. For backward compatibility or advanced use cases, developers might explicitly set ARIA roles using the role attribute. However, setting an invalid role can lead to accessibility issues, as seen with trying to assign navigation to a ul element.

Instead of applying the navigation role to a ul directly, wrap your ul with a nav element.

The allowed ARIA roles for an ul element are directory, group, listbox, menu, menubar, none, presentation, radiogroup, tablist, toolbar and tree, but not navigation.

Examples

Here is how you can use the nav element with a ul.

<nav>
  <ul>
    <li><a href="#home">Home</a></li>
    <li><a href="#about">About</a></li>
    <li><a href="#contact">Contact</a></li>
  </ul>
</nav>

There’s no role in ARIA named presentational, you probably mean presentation.

The presentation role and its synonym none remove an element’s implicit ARIA semantics from being exposed to the accessibility tree.

The content of the element will still be available to assistive technologies; it is only the semantics of the container — and in some instance, required associated descendants — which will no longer expose their mappings to the accessibility API.

The role attribute in HTML is used to define the accessibility role of an element, which helps assistive technologies understand the purpose or type of the element. The value tabpanel is not appropriate for a <ul> element, which is used for unordered lists.

The role of tabpanel is intended to be used with elements that represent a tab panel, which is part of a tabbed interface. A tabbed interface consists of elements with roles like tablist, tab, and tabpanel. Typically, tabpanel is used with containers that house the content associated with a tab, such as a <div>.

To fix this error, ensure that the tabpanel role is applied to the correct element. Here’s a simple example of how a tab interface can be structured correctly:

<div role="tablist" aria-label="Sample Tabs">
  <button role="tab" aria-controls="panel-1" id="tab-1">Tab 1</button>
  <button role="tab" aria-controls="panel-2" id="tab-2">Tab 2</button>
</div>

<div role="tabpanel" id="panel-1" aria-labelledby="tab-1" hidden>
  <p>Content for Tab 1.</p>
</div>

<div role="tabpanel" id="panel-2" aria-labelledby="tab-2" hidden>
  <p>Content for Tab 2.</p>
</div>

In this example:

• The role tablist is applied to the container element that directly contains the tab elements.
• Each button serving as a tab has the role of tab.
• Each tab panel, which contains the content for a tab, has the role of tabpanel.

Avoid using tabpanel on non-semantic or incorrectly associated elements like <ul>. Instead, use elements like <div> or <section> for tab panels, ensuring the roles align with the intended roles in a tabbed interface.

The sizes attribute for an img element requires valid CSS syntax, and auto is not an acceptable value within that attribute.

The sizes attribute allows you to specify a list of media conditions and corresponding sizes for the images. Each condition determines which size of the image should be displayed at different viewport widths, ensuring responsive image delivery. The syntax for sizes should be a comma-separated list of media queries followed by a value denoting the corresponding width of the image. This width value may be in pixels (px) or as a percentage (vw, vh), but auto is not valid in this context.

Here is a breakdown of a correct sizes attribute usage:

• 50vw: This denotes that the image should take up 50% of the viewport’s width.
• (max-width: 600px) 100vw, 50vw: When the viewport is at most 600 pixels wide, the image should occupy the full width (100vw). Otherwise, it should take 50 percent of the viewport width.

Remove “auto” from your sizes value and provide a valid, contextually correct CSS value.

Example

<!DOCTYPE html>
<html lang="en">
<head>
  <title>Responsive Images Example</title>
</head>
<body>
  <img
    src="image.jpg"
    sizes="(max-width: 472px) 100vw, 472px"
    srcset="image-small.jpg 300w, image-medium.jpg 600w, image-large.jpg 1000w"
    alt="A description of the image"
  >
</body>
</html>

In this example, if the viewport width is less than or equal to 472 pixels, the image will take up the entire width (100vw). For larger widths, the srcset specifies different image files for varying resolutions.

The sizes attribute on the img element must use CSS length units (such as px, vw, em) and not image width descriptors like w.

The sizes attribute defines the intended display size of the image in CSS length units, which helps the browser select the appropriate image from the srcset. Use units like px (pixels) or vw (viewport width percentage), not w, which is used in the srcset descriptors. The srcset attribute specifies different image resources and their width descriptors (e.g., 860w), while sizes reflects the image’s display size in the layout.

Correct usage:

• sizes="(min-width: 568px) 140px" tells the browser the image will be displayed as 140 pixels wide when the viewport is at least 568 pixels wide.
• srcset="photo.png?w=860&q=90 860w" uses w as the descriptor for the image resource’s width.

HTML example:

<img
  alt=""
  sizes="(min-width: 568px) 140px"
  srcset="photo.png?w=860&amp;q=90 860w"
  src="photo.png?w=860&amp;q=90">

Summary:

• Use CSS units like px, vw, etc. in the sizes attribute.
• Use the w descriptor only in srcset, not in sizes.