HTML Checking for Large Sites
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Bad value “X” for attribute “src” on element “img”: Illegal character in scheme data: space is not allowed.
The src attribute on an <img> tag is not allowed to contain space characters. You should replace them with “%20“.
Related W3C validator issues
The <script> tag allows authors to include dynamic scripts and data blocks in their documents. When the src is present, this tag accepts a type attribute which must be either:
- an empty string
-
text/javascript(that’s the default, so it can be omitted) -
module
Examples:
<!-- This is valid, without a type it defaults to JavaScript -->
<script src="app.js"></script>
<!-- This is valid, but will warn that it can be omitted -->
<script type="text/javascript" src="app.js"></script>
<!-- An empty attribute is valid, but will warn that it can be omitted -->
<script type="" src="app.js"></script>
<!-- The module keyword is also valid as a type -->
<script type="module" src="app.js"></script>
<!-- Any other type is invalid -->
<script type="wrong" src="app.js"></script>
<script type="text/html" src="app.js"></script>
<script type="image/jpeg" src="app.js"></script>
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<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:
<img src="photo.jpg" alt="Person holding a cat" />
When an img element has an empty alt attribute, its role is implicitly decorative, so it must not specify a role attribute.
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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>
</html>
Learn more:
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The href attribute of an <a> element contains an invalid character, that should be properly encoded as a URI percent-encoded character.
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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>
Learn more:
The src attribute on an <img> element contains an invalid character, that should be properly encoded as a URI percent-encoded character.
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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 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.
Learn more:
The accept attribute may be specified to provide browsers with a hint of what file types will be accepted on an <input> element. It expects a comma-separated list of allowed file types. Refer to the list of media types to check the accepted tokens. In this example, the first line is invalid while the second is valid:
<input name='file' type='file' accept='doc, docx, pdf' />
<input name='file' type='file' accept='text/doc, text/docx, application/pdf' />
Space characters are not allowed in href attributes. Instead, they should be converted to %20. In this example, the first line is invalid and the second is valid:
<a href="https://example.com#some term">invalid</a>
<a href="https://example.com#some%20term">valid</a>
The href attribute on an <a> tag contains an space, which is not allowed. Consider replacing space characters with “%20”.
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 query part of that URL contains one or more space characters, which are not allowed, for example:
<iframe src="https://maps.google.it/maps?q=2700 6th Avenue"></iframe>
You should properly escape all space characters as %20 like this:
<iframe src="https://maps.google.it/maps?q=2700%206th%20Avenue"></iframe>
Learn more:
The src attribute on an element <img> contains a { curly bracket character, which is not allowed unless properly encoded.
Space characters are not allowed in src attributes. Instead, they should be converted to %20. In this example, the first line is invalid and the second is valid:
<img src="https://example.com/?s=some term" alt="description" />
<img src="https://example.com/?s=some%20term" alt="description" />
The src attribute on an element <img> contains a character that is not allowed, and should be encoded.
Some typical examples include the pipe character | that should be replaced by its encoded alternative %7C , and the left square bracket [ that needs to be encoded as %5B.
The attributes width and height on <img> elements define the dimensions of the image in CSS pixels, and expect a non-negative integer.
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<img> elements accept a width attribute to specify the size in pixels. This value can only be an integer, it should not contain units or %. If you need to specify a percentage width, you can do that with CSS:
<img src="photo.jpg" alt="red car" style="width:100%;">
The width and height attributes on <img> and <iframe> elements expect a digit to indicate the number of pixels. Ensure that this attribute contains only digits.
For example:
<!-- This is invalid because width is not a digit -->
<img width="225px" height="100px" alt="cat" src="cat.jpg" />
<!-- This is valid -->
<img width="225" height="100" alt="cat" src="cat.jpg" />
<img> tags used to display images require the attribute src to indicate the source of the image, for example <img src="/img/photo.jpg" />.
An HTML tag could not be parsed, most probably because of a typo.
The async and defer boolean attributes of the <script> element control how an external script should be executed once it has been downloaded. The async attribute makes sense when an external script (defined with the src attribute) is loaded, or when defining a script of type module:
<script async src="app.js"></script>
<script type="module">
/* JavaScript module code here */
</script>
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The charset attribute on a <script> element can be used to specify the character encoding of an external script, whose URL should be specified on the src attribute.
If the script is not external, then the charset attribute should not be used, as the character encoding of the HTML document will be used.
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The defer and async boolean attributes of the <script> element control how an external script should be executed once it has been downloaded. These attributes only make sense when referring to external scripts, so a src attribute must also be present to specify the location of the script.
Example:
<script defer src="app.js"></script>
If your script is not external, and is inlined within the HTML document, then you should remove the defer attribute, like in this example:
<script>
console.log("hello");
</script>
Learn more:
A character has been found in the document that is not allowed in the charset encoding being used.
The document has been declared to use a windows-1251 charset but the actual contents seems to be utf-8. You should update the charset to that like in this example:
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
The document could not be properly parsed due to malformed characters. Check the document encoding.
Read about Normalization in HTML and CSS.
<img> tags no longer accept a border attribute. This can be defined using CSS instead, for example:
<img src="..." alt="..." style="border:0;" />
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:
Read about Normalization in HTML and CSS.
Check the HTMLImageElement.srcset guide to learn about the correct usage of the srcset and sizes attributes.
Still checking your large sites one page at a time?
Save time using our automated web checker. Let our crawler check your web pages on the W3C Validator.