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The “complementary” role is unnecessary for element “aside”.
Using the <aside> element will automatically communicate a section has a role of complementary, so specifying the role="complementary" is redundant.
Related W3C validator issues
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>Learn more:
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>Learn more at:
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.
Learn more:
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.
Learn more about the alert ARIA role:
A <li> element, used to define a list item, does not accept the button role.
This HTML code is invalid because the <li> elements can’t have role="button":
<ul>
<li role="button">One</li>
<li role="button">Two</li>
</ul>Learn more:
<input> elements can’t have a search role. Instead, try with <input type="search">.
<input> elements of type search are text fields designed for the user to enter search queries into. These are functionally identical to text inputs, but may be styled differently depending on the user agent.
The search role is a landmark. Landmarks can be used by assistive technology to quickly identify and navigate to large sections of the document. The search role is added to the container element that encompasses the items and objects that, as a whole, combine to create search functionality. When a <form> is a search form, use the search role on the form.
Example of a search form:
<form role="search">
<label for="search-input">Search this site</label>
<input type="search" id="search-input" name="search">
<input value="Submit" type="submit">
</form>Learn more:
The <a> element requires either a href attribute, or a role attribute.
Learn more:
An element is using ARIA attributes, but its role has not been defined. ARIA defines semantics that can be applied to elements, with these divided into roles (defining a type of user interface element) and states and properties that are supported by a role. Authors must assign an ARIA role and the appropriate states and properties to an element during its life-cycle, unless the element already has appropriate ARIA semantics (via use of an appropriate HTML element). Examples:
<!-- This div uses ARIA but its role is not clear, so it's invalid. -->
<div aria-expanded="true">...</div>
<!-- This div defines clearly its role, so it's valid. -->
<div role="navigation" aria-expanded="true">...</div>
<!-- Nav elements have an implicit navigation role so we don't need the role attribute. -->
<nav aria-expanded="true">...</nav>
Read about Using ARIA: Roles, states and properties.
The article role indicates a section of a page that could easily stand on its own on a page, in a document, or on a website, is implicit when using the <article> tag.
This role indicates a section of a page that could easily stand on its own on a page, in a document, or on a website. It is usually set on related content items such as comments, forum posts, newspaper articles or other items grouped together on one page. It can be added to generic elements like <div> to convey this role, for example:
<div role="article">
<h2>Heading</h2>
<p>Content...</p>
</div>
Instead of using this role, it’s preferrable to use the native <article> element like this:
<article>
<h2>Heading</h2>
<p>Content...</p>
</article>Learn more:
The <header> HTML element represents introductory content, typically a group of introductory or navigational aids, and has an implicit role of banner, so specifying this role is redundant.
The following example represents a banner using the role attribute:
<div role="banner">
<img src="companylogo.svg" alt="my company name" />
<h1>Title</h1>
<p>Subtitle</p>
</div>
By default, the HTML5 <header> element has an identical meaning to the banner landmark, unless it is a descendant of <aside>, <article>, <main>, <nav>, or <section>, at which point <header> is the heading for that section and not the equivalent of the site-wide banner.
This example uses the <header> element instead of the banner role:
<header>
<img src="companylogo.svg" alt="my company name" />
<h1>Title</h1>
<p>Subtitle</p>
</header>
The button role is used to make an element appear as a button control to a screen reader and can be applied to otherwise non-interactive elements like <div>. If you’re already using a <button> element, then it’s redundant to apply it the role button, as that’s implicit.
<!-- Instead of this -->
<button role="button">Buy</button>
<!-- Do this -->
<button>Buy</button>
Learn more:
The <summary> HTML element specifies a clickable summary, caption, or legend for a <details> element’s disclosure box. As the <summary> element has an implicit button role, it’s not needed to include it explicitly.
Here’s an example, clicking the <summary> element toggles the state of the parent <details> element open and closed.
<details>
<summary>I have keys but no doors. I have space but no room. You can enter but can’t leave. What am I?</summary>
A keyboard.
</details>Learn more:
The <footer> element represents a footer for its nearest sectioning content, and has an implicit role of contentinfo, so specifying this role is redundant.
The following example marks a <div> as a footer specifying its role:
<div role="contentinfo">
<h2>Footer</h2>
<!-- footer content -->
</div>
Using the <footer> element instead is recommended:
<footer>
<h2>Footer</h2>
<!-- footer content -->
</footer>Lear more:
MDN: ARIA contentinfo role MDN: footer * HTML Spec: the footer element
A <form> element has already a form role, so specifying role="form" in it is redundant.
Instead of:
<form role="form">
You can simply write:
<form>
The heading role defines this element as a heading to a page or section, and is implicit in tags <h1> to <h6>.
The heading role indicates to assistive technologies that this element should be treated like a heading. Screen readers would read the text and indicate that it is formatted like a heading.
This ARIA role is only needed to add that role to a generic element like <div>, for example:
<div role="heading" aria-level="1">This is a main page heading</div>
This defines the text in the <div> to be the main heading of the page, indicated by being level 1 via the aria-level attribute. Opt for using the <h1> (thru <h6>) element instead:
<h1>This is a main page heading</h1>
Learn more:
A single <img> element is used to embed an image, so adding the img role to it is redundant.
The ARIA img role can be used to identify multiple elements inside page content that should be considered as a single image. These elements could be images, code snippets, text, emojis, or other content that can be combined to deliver information in a visual manner, for example:
<div role="img" aria-label="Description of the overall image">
<img src="graphic1.png" alt="">
<img src="graphic2.png">
</div>Learn more:
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>Read more:
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>Read more:
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>Read more about the nav element and the ARIA Navigation Role.
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.
Learn more:
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