HTML Checking for Large Sites
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Check the HTMLImageElement.srcset guide to learn about the correct usage of the srcset and sizes attributes.
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Related W3C validator issues
The sizes attribute specifies the size of the image when it is displayed on different devices.
The error message is saying that the value auto is not a valid value for the sizes attribute.
To fix this issue, you need to replace the value auto with a valid size. You can use a width descriptor or a media query to specify the size for different device widths.
Here’s an example of using a width descriptor:
<img src="example.jpg" sizes="(max-width: 600px) 100vw, 50vw" />This example sets the size of the image to 100% of the viewport width when the device width is less than or equal to 600px, and 50% of the viewport width for larger device widths.
Alternatively, you can remove the sizes attribute altogether and let the browser decide the best size for the image based on the viewport size.
<img src="example.jpg" />If you do this, the browser will use the default sizes value of 100vw and will scale the image accordingly.
The srcset property on img elements, when used, requires at least one value. This property is a string which identifies one or more image candidate strings, separated using commas (,) each specifying image resources to use under given circumstances.
Each image candidate string contains an image URL and an optional width or pixel density descriptor that indicates the conditions under which that candidate should be used instead of the image specified by the src property.
Example:
<img
src="/img/cat-200px.png"
alt="Cat"
srcset="
/img/cat-200px.png 1x,
/img/cat-400px.png 2x
">The sizes attribute is used to complement the srcset attribute on an <img> tag for responsive images, therefore it’s not valid if srcset is missing.
<img> tags, used to include images on a document, require an alt attribute to describe the contents of the image. This is essential for users that cannot see the image (like screen reader users), or as an alternate text when the image cannot be displayed. Example:
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When an img element has an empty alt attribute, its role is implicitly decorative, so it must not specify a role attribute.
A start tag for <img> has been found inside a <noscript> section within the <head>, where it’s not allowed. Consider moving it to the <body> section.
The HTML <noscript> element defines a section of HTML to be inserted if a script type on the page is unsupported or if scripting is currently turned off in the browser.
When JavaScript is disabled, the content inside <noscript> will be used instead, so this content must fit within its parent section. As an <img> tag is not allowed inside <head>, this will raise an issue. Instead, consider moving the <noscript> part to the <body> section.
This issue is often related to 3rd party tracking pixels like the Facebook or LinkedIn conversion tracking pixels. For example, the Facebook pixel instructions tell you to insert it like this:
<html>
<head>
<script>
...some script...
</script>
<noscript>
<img src="..." />
</noscript>
</head>
<body>
...
</body>
</html>Instead, consider moving the <noscript> part inside the <body>, where the <img> makes sense to be inserted:
<html>
<head>
<script>
...some script...
</script>
</head>
<body>
...
<noscript>
<img src="..." />
</noscript>
</body>
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The src attribute on an <img> element contains an invalid character, that should be properly encoded as a URI percent-encoded character.
The src attribute for <img> tags is required, to define the source of the image, like in this example:
<img src="photo.jpg" alt="wombat" />The sizes attribute is used to complement the srcset attribute on an <img> tag for responsive images. When this attribute is present, all image candidates must specify its width.
The attributes width and height of <img> elements expect a non-negative integer, so an empty string is not allowed. Either define the correct dimension, or remove this attribute.
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