HTML Guide
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
longdescattribute is used on theiframeelement, which is now obsolete. -
Updated Code: We remove the
longdescattribute and provide an external link using theaelement to guide users to the description.
Learn more:
Related W3C validator issues
The <iframe> HTML element represents a nested browsing context, embedding another HTML page into the current one.
As the iframe is a container that holds an embedded HTML page, it cannot be nested inside an a tag.
A button element, or an element with the role=button attribute, is not allowed to be nested inside an <a> element.
An <a> element cannot contain a descendant element with the attribute tabindex.
The seamless attribute was proposed to be included in the HTML5 spec, but it wasn’t finally accepted, so it’s not a valid attribute for <iframe>.
There is an iframe tag inside a noscript tag that is itself inside the head section of the HTML document. This is not allowed because an iframe cannot be nested inside the head section.
To fix this issue, you may move the noscript section that contains the iframe tag outside of the head section, and ensure that it is placed within the body section of the HTML document.
For example, this is invalid HTML because the head section cannot contain iframe elements:
<!DOCTYPE html>
<html lang="en">
<head>
<title>My webpage</title>
<noscript>
<p>Please enable JavaScript to view this website</p>
<iframe src="https://example.com/"></iframe>
</noscript>
<!-- Other meta tags and styles go here -->
</head>
<body>
<!-- Rest of your webpage content goes here -->
</body>
</html>Moving the noscript inside the body section fixes the issue, as that’s where iframe elements belong:
<!DOCTYPE html>
<html lang="en">
<head>
<title>My webpage</title>
<!-- Other meta tags and styles go here -->
</head>
<body>
<noscript>
<p>Please enable JavaScript to view this website</p>
<iframe src="https://example.com/"></iframe>
</noscript>
<!-- Rest of your webpage content goes here -->
</body>
</html>The href attribute of an <a> element contains an invalid character, that should be properly encoded as a URI percent-encoded character.
An <iframe> element allows to embed an HTML document inside another HTML document, and its src attribute is indicated the source URL of the embedded web page. The src attribute is a required attribute, so it cannot be blank.
Example:
<iframe src="https://example.com/map.html"></iframe>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 attributes width and height of <iframe> elements expect a non-negative integer, so an empty string is not allowed. Either define the correct dimension, or remove this attribute.
The href attribute on an a tag expects a valid URL, but only http(s):// was found.