Bad value “complimentary” for attribute “role” on element “aside”.

Using the <aside> element will automatically communicate a section has a role of complementary, so specifying the role="complementary" is redundant.

There can only be one visible <main> element in a document. If more are needed (for example for switching between them with JavaScript), only one can be visible, the others should be hidden toggling the hidden attribute.

Example of 2 main elements, where only one is visible:

<main>
  <h1>Active main element</h1>
<!-- content -->

</main>

<main hidden>
  <h1>Hidden main element</h1>
<!-- content -->

</main>

The HTML <figure> element is used to encapsulate media content, such as an image or graphic, along with a descriptive <figcaption>. When a <figcaption> is present within a <figure>, it inherently provides the semantics of the <figure>, making it self-explanatory without needing an additional role attribute.

Explanation

• <figure> element: Represents self-contained content, potentially with an optional caption specified by a <figcaption> element. This is inherently recognized for its semantics as a figure with a caption.

• <figcaption> element: Provides a caption or description for the content of the <figure>. This helps in describing the media or content included in the <figure> element.

• role attribute: This attribute is used to define an explicit accessibility role for an element. However, in cases where the element’s native semantics are explicit and sufficient, such as a <figure> with a <figcaption>, adding a role attribute might override or conflict with the inherent meaning.

Solution

Remove the role attribute from the <figure> element when it contains a <figcaption>.

Example of Incorrect Code:

<figure role="figure">
  <img src="cat.jpg" alt="A cute cat">
  <figcaption>A cute cat looking at the camera.</figcaption>
</figure>

Corrected Code:

<figure>
  <img src="cat.jpg" alt="A cute cat">
  <figcaption>A cute cat looking at the camera.</figcaption>
</figure>

In the corrected example, the <figure> element does not have a role attribute, allowing it to maintain its inherent semantic value.

A role="cell" element must be a child of an element with role="row" for correct ARIA relationships.

According to the ARIA specification, role="cell" should be directly contained within a parent with role="row", which itself should usually be inside an element with role="rowgroup" or role="table". This structure allows assistive technologies to interpret your table semantics correctly.

Correct Structure Example:

<div role="table">
  <div role="row">
    <div role="cell">Row 1, Cell 1</div>
    <div role="cell">Row 1, Cell 2</div>
  </div>
  <div role="row">
    <div role="cell">Row 2, Cell 1</div>
    <div role="cell">Row 2, Cell 2</div>
  </div>
</div>

Incorrect Structure Example (missing row):

<div role="table">
  <div role="cell">Cell without row</div>
</div>

How to fix:
Wrap any element with role="cell" inside an element with role="row". This ensures both validity and proper accessibility support.

A role="columnheader" element must be a child of or associated with a role="row" element.

In HTML, ARIA roles such as columnheader are used to improve accessibility for assistive technologies. According to the ARIA specification, a columnheader role should appear inside an element with role="row", which itself should be inside an element with role="table" or role="grid". This structure mimics how native tables are constructed with <th> elements inside <tr>s.

Correct structure:

• role="table" or role="grid" contains one or more elements with role="row".
• Each role="row" contains one or more elements with role="columnheader" (or role="cell").

Example using ARIA roles for a simple table:

<div role="table" aria-label="Sample Table">
  <div role="row">
    <div role="columnheader">Name</div>
    <div role="columnheader">Age</div>
  </div>
  <div role="row">
    <div role="cell">Alice</div>
    <div role="cell">30</div>
  </div>
</div>

Best practice:
Whenever possible, use native table elements, which have built-in roles and accessibility, reducing the chance of ARIA misuse.

Example using native table markup:

<table>
  <tr>
    <th>Name</th>
    <th>Age</th>
  </tr>
  <tr>
    <td>Alice</td>
    <td>30</td>
  </tr>
</table>

Ensure that any element with role="columnheader" is always contained within a parent with role="row". Avoid placing role="columnheader" directly inside a container without the appropriate role="row" ancestor.

To fix the W3C HTML Validator issue stating that an element with a role="menuitem" must be contained in, or owned by, an element with role="menubar" or role="menu", you need to ensure that your menuitem elements are properly nested within a menubar or menu element. This is important for accessibility, as it helps assistive technologies understand the structure and relationship of the elements.

The menuitem role indicates the element is an option in a set of choices contained by a menu or menubar.

Here is a step-by-step guide to fixing this issue:

1. Using role="menubar"

If your menuitem elements are part of a horizontal menu (like a navigation bar), they should be nested within an element with role="menubar".

Example:

<nav role="menubar">
  <div role="menuitem">Home</div>
  <div role="menuitem">About</div>
  <div role="menuitem">Contact</div>
</nav>

2. Using role="menu"

If your menuitem elements are part of a submenu or a vertical menu, they should be contained within an element with role="menu".

Example:

<div role="menu">
  <div role="menuitem">Item 1</div>
  <div role="menuitem">Item 2</div>
  <div role="menuitem">Item 3</div>
</div>

Ensuring Proper Nesting

Ensure that all your menuitem elements are either directly or indirectly (via a child-parent relationship) contained within a menubar or menu element.

Complete Example with Nested Menus:

Here is a more complex example, including nested menus for a drop-down scenario.

Example:

<nav role="menubar">
  <div role="menuitem">Home</div>
  <div role="menuitem">
    About
    <div role="menu">
      <div role="menuitem">Team</div>
      <div role="menuitem">History</div>
    </div>
  </div>
  <div role="menuitem">Contact</div>
</nav>

In this example, the main navigation (menubar) contains menuitem elements, and one of those menuitem elements contains a nested menu with additional menuitem elements inside it.

By ensuring your menuitem elements are contained within appropriate parent elements (menubar or menu), you will resolve the W3C HTML Validator issue and improve your web page’s accessibility.

Elements with the role tab must either be a child of an element with the tablist role, or have their id part of the aria-owns property of a tablist.

An element with the tab role controls the visibility of an associated element with the tabpanel role. The common user experience pattern is a group of visual tabs above, or to the side of, a content area, and selecting a different tab changes the content and makes the selected tab more prominent than the other tabs.

Example:

<div class="tabs">
  <div role="tablist" aria-label="Sample Tabs">
    <button role="tab" aria-selected="true" aria-controls="panel-1" id="tab-1" tabindex="0">
          First Tab
    </button>
    <button role="tab" aria-selected="false" aria-controls="panel-2" id="tab-2" tabindex="-1">
          Second Tab
     </button>
  </div>
  <div id="panel-1" role="tabpanel" tabindex="0" aria-labelledby="tab-1">
    <p>Content for the first panel</p>
  </div>
  <div id="panel-2" role="tabpanel" tabindex="0" aria-labelledby="tab-2" hidden>
    <p>Content for the second panel</p>
  </div>
</div>

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

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

The alert role can be used to tell the user an element has been dynamically updated. Screen readers will instantly start reading out the updated content when the role is added. The element <ul> doesn’t accept this kind of role, consider using other element like <p> or <div>.

The alert role is used to communicate an important and usually time-sensitive message to the user. When this role is added to an element, the browser will send out an accessible alert event to assistive technology products which can then notify the user about it. The alert role is most useful for information that requires the user’s immediate attention.