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Related W3C validator issues
A button element, or an element with the role=button attribute, is not allowed to be nested inside an <a> element.
An a element is not allowed to be nested inside a <button> element, or an element with the role=button attribute.
An <a> element cannot contain a descendant element with the attribute tabindex.
A button element cannot contain a descendant element with the attribute tabindex.
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The aria-expanded attribute can only be true, false, or undefined.
This attribute indicates whether a grouping element is expanded or collapsed.
An element like <h1>, <h2>, etc., used to define a heading, does not accept the button role.
The following HTML code is invalid because the <h2> element can’t have role="button"
<h2 role="button">Some heading</h2>
Instead, you can nest the <h2> inside a <div> with that role. In this case however, browsers automatically apply role presentation to all descendant elements of any button element as it is a role that does not support semantic children.
<div role="button"> <h2>Some heading</h2> </div>
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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>
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.
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