HTML Guide
The <meta charset> is expected to appear at the beginning of the document, within the first 1024 bytes. Consider moving it to the beginning of the <head> section, as in this example:
<head>
<meta charset="utf-8">
...
</head>A character encoding declaration is a mechanism by which the character encoding used to store or transmit a document is specified. For HTML documents, the standard way to declare a document character encoding is by including a <meta> tag with a charset attribute, typically <meta charset="utf-8">.
According to the W3C standard:
The element containing the character encoding declaration must be serialized completely within the first 1024 bytes of the document.
In order to define the charset encoding of an HTML document, both of these options are valid, but only one of them must appear in the document:
<!-- This is the preferred way -->
<meta charset="UTF-8">
<!-- This is the older way, also valid -->
<meta http-equiv="content-type" content="text/html; charset=UTF-8">The <meta charset> tag, used to define the character encoding, must appear only once in a document, within the <head> section.
Remove duplicate <meta> elements that set the name attribute to description from your HTML document.
HTML documents should only include one <meta> element with the name attribute set to description to provide a brief summary of the webpage content. This is crucial for search engine optimization, as search engines use this information to display summaries of your pages in search results. A duplicate description meta tag can confuse search engines, possibly affecting your webpage’s visibility negatively. To resolve this, locate all <meta> elements with name="description" in your HTML and remove duplicates, leaving only one that accurately describes your content.
Example of Duplicate Meta Tags
<!DOCTYPE html>
<html lang="en">
<head>
<title>Sample Page</title>
<meta name="description" content="This is a description of the page.">
<meta name="description" content="Another description here.">
<meta name="author" content="John Doe">
</head>
<body>
<h1>Welcome to the Sample Page</h1>
<p>This page serves as an example for HTML structure.</p>
</body>
</html>Corrected Version
<!DOCTYPE html>
<html lang="en">
<head>
<title>Sample Page</title>
<meta name="description" content="This is a description of the page.">
<meta name="author" content="John Doe">
</head>
<body>
<h1>Welcome to the Sample Page</h1>
<p>This page serves as an example for HTML structure.</p>
</body>
</html>Ensure that the content for the description meta tag is meaningful and relevant to what visitors can expect to find on the web page.
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>The HTML <figure> element is used to encapsulate media content, such as an image or graphic, along with a descriptive <figcaption>. When a <figcaption> is present within a <figure>, it inherently provides the semantics of the <figure>, making it self-explanatory without needing an additional role attribute.
Explanation
-
<figure> element: Represents self-contained content, potentially with an optional caption specified by a <figcaption> element. This is inherently recognized for its semantics as a figure with a caption.
-
<figcaption> element: Provides a caption or description for the content of the <figure>. This helps in describing the media or content included in the <figure> element.
-
role attribute: This attribute is used to define an explicit accessibility role for an element. However, in cases where the element’s native semantics are explicit and sufficient, such as a <figure> with a <figcaption>, adding a role attribute might override or conflict with the inherent meaning.
Solution
Remove the role attribute from the <figure> element when it contains a <figcaption>.
Example of Incorrect Code:
<figure role="figure">
<img src="cat.jpg" alt="A cute cat">
<figcaption>A cute cat looking at the camera.</figcaption>
</figure>Corrected Code:
<figure>
<img src="cat.jpg" alt="A cute cat">
<figcaption>A cute cat looking at the camera.</figcaption>
</figure>In the corrected example, the <figure> element does not have a role attribute, allowing it to maintain its inherent semantic value.
A <link> element has been found in an invalid body context. Check the attributes of the <link> element and ensure it’s not within the <body> section.
If the element is within the <head> section, it may have been interpreted as a body context depending on previous elements. For example, while this <link> element is valid per se and is in the <head> section, it is deemed invalid because the previous <img> element made the validator consider it a body context:
<!DOCTYPE html>
<html lang="">
<head>
<title>Test</title>
<img src="photo.jpg" alt="A smiling cat" />
<link rel="canonical" href="https://example.com/" />
</head>
<body>
<p>Some content</p>
</body>
</html>If we fix that document and move the <img> tag within the body, the issue raised about <meta> disappears because it’s now in a valid context:
<!DOCTYPE html>
<html lang="">
<head>
<title>Test</title>
<link rel="canonical" href="https://example.com/" />
</head>
<body>
<p>Some content</p>
<img src="photo.jpg" alt="A smiling cat" />
</body>
</html>A <link> element that is using the preload value in the rel attribute is missing the as attribute, used to indicate the type of the resource.
The preload value of the <link> element’s rel attribute lets you declare fetch requests in the HTML’s <head>, specifying resources that your page will need very soon, which you want to start loading early in the page lifecycle, before browsers’ main rendering machinery kicks in. This ensures they are available earlier and are less likely to block the page’s render, improving performance.
The as attribute specifies the type of content being loaded by the <link>, which is necessary for request matching, application of correct content security policy, and setting of correct Accept request header.
The error message indicates that the <link> element contains an as attribute, but its rel attribute does not hold the correct value. According to the HTML specification, when using the as attribute, the rel attribute must be set to "preload" or "modulepreload".
Explanation
The as attribute is used to specify the type of content being loaded, which helps the browser to handle it appropriately. To preload resources, you need to specify the rel attribute with the value "preload" (for general resources) or "modulepreload" (specifically for JavaScript modules).
Example with preload:
If you are preloading a stylesheet, the rel attribute should be set to "preload":
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Correct Usage of Link with as Attribute</title>
<link rel="preload" href="styles.css" as="style">
</head>
<body>
<p>Hello, World!</p>
</body>
</html>Example with modulepreload:
If you are preloading a JavaScript module, the rel attribute should be set to "modulepreload":
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Correct Usage of Link with Modulepreload</title>
<link rel="modulepreload" href="script.js" as="script">
</head>
<body>
<p>Hello, World!</p>
</body>
</html>The only value admitted for the attribute content in a <meta http-equiv="X-UA-Compatible"> is currently IE=edge. You’re probably seeing this issue because the page being validated includes the following meta tag:
<meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1" /> As the Google Chrome Frame plugin was discontinued on February 25, 2014, this is longer supported so you should change that meta tag to:
<meta http-equiv="X-UA-Compatible" content="IE=edge" /> According to this article in Wikipedia:
Google Chrome Frame was a plug-in designed for Internet Explorer based on the open-source Chromium project, first announced on September 22, 2009. It went stable in September 2010, on the first birthday of the project. It was discontinued on February 25, 2014 and is no longer supported.
The plug-in worked with Internet Explorer 6, 7, 8 and 9. It allowed suitably coded web pages to be displayed in Internet Explorer by Google Chrome’s versions of the WebKit layout engine and V8 JavaScript engine.
According to the HTML specification, text must not contain control characters other than space characters.
In particular, the control character 
escapes the Unicode control character “CARRIAGE RETURN” are not allowed.
An alternative is using the character reference which escapes the Unicode control character “LINE FEED” that is defined to be a space character, so it’s allowed in HTML text.
The combination of type="module" and defer is not allowed. The type="module" attribute itself implies that the script should be executed in a deferred way, hence using the defer attribute is unnecessary and invalid.
Steps to Fix the Issue:
- Remove the defer Attribute: When you use type="module", you should not include the defer attribute since module scripts defer automatically.
Incorrect Code:
<script type="module" defer src="example.js"></script>Corrected Code:
<script type="module" src="example.js"></script>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>The W3C HTML validator issue arises when a <select> element is marked as required but doesn’t contain any <option> elements. The semantic purpose of a <select> element is to provide a list of options for the user to select from. If it is marked as required, it implies the user must make a selection from available options.
Here is an explanation of the involved elements and attributes:
-
<select>: This represents a drop-down list in an HTML form.
- required: When this attribute is present, it means the user must select an option before submitting the form. It cannot be empty.
- multiple: This boolean attribute allows multiple selections if present.
- size: This attribute specifies the number of visible options. If greater than 1 and multiple is not set, it turns the drop-down into a list box.
If the multiple attribute is not present and the size attribute is not greater than 1, you need at least one <option> element for the <select> to be valid when required is used.
To resolve this, ensure that your <select> element contains at least one <option>:
<label for="choices">Choose an option:</label>
<select id="choices" name="choices" required>
<option value="">--Please choose an option--</option>
<option value="option1">Option 1</option>
<option value="option2">Option 2</option>
</select>This example includes a placeholder option with an empty value to prompt the user to select an option and other valid options. The value for the placeholder is empty, which is a common practice for required fields to prevent it from being selected by default.
An HTML tag could not be parsed, most probably because of a typo.
Table rows on the same <table> element must have the same number of columns, which comes determined by the first tr row.
For example, this table is wrong as the first row defines 2 columns, while the second row tries to use 4 columns:
<table>
<tr>
<td>Liza</td>
</tr>
<tr>
<td>Jimmy</td>
<td>14</td>
</tr>
</table>A <table> contains a <tr> row that has less <td> columns than the column count established by the first row. Check the table to ensure all rows have the same number of columns.
For example, in the following table, the first <tr> row defines that it’s 2 columns wide, but the second <tr> row tries to use only 1 column:
<table>
<!-- This first row sets the table as 2 columns wide -->
<tr>
<td>First</td>
<td>Second</td>
</tr>
<!-- This second row has only 1 column -->
<tr>
<td>Wrong</td>
</tr>
</table>Rocket Validator checks HTML on your sites using the latest version of W3C Validator Nu HTML Checker, which is intended for HTML5 documents.
The page scanned is using an “almost standards mode” doctype, instead of the expected <!DOCTYPE html>. While the almost standards mode was used in the transition to HTML5, you should consider moving to the HTML5 standard.
To fix this issue, ensure that an element with role="listitem" is contained within an element with role="list" or role="group". Here’s how you can structure your HTML correctly:
Incorrect Example
<div role="listitem">Item 1</div>
<div role="listitem">Item 2</div>Correct Example
<div role="list">
<div role="listitem">Item 1</div>
<div role="listitem">Item 2</div>
</div>Alternatively, you can use role="group" if it’s a nested list.
Correct Example with Nested List
<div role="list">
<div role="listitem">Item 1</div>
<div role="group">
<div role="listitem">Item 1.1</div>
<div role="listitem">Item 1.2</div>
</div>
<div role="listitem">Item 2</div>
</div>This ensures that the role="listitem" elements are correctly contained.
To fix the W3C HTML Validator issue stating that an element with a role="menuitem" must be contained in, or owned by, an element with role="menubar" or role="menu", you need to ensure that your menuitem elements are properly nested within a menubar or menu element. This is important for accessibility, as it helps assistive technologies understand the structure and relationship of the elements.
The menuitem role indicates the element is an option in a set of choices contained by a menu or menubar.
Here is a step-by-step guide to fixing this issue:
1. Using role="menubar"
If your menuitem elements are part of a horizontal menu (like a navigation bar), they should be nested within an element with role="menubar".
Example:
<nav role="menubar">
<div role="menuitem">Home</div>
<div role="menuitem">About</div>
<div role="menuitem">Contact</div>
</nav>2. Using role="menu"
If your menuitem elements are part of a submenu or a vertical menu, they should be contained within an element with role="menu".
Example:
<div role="menu">
<div role="menuitem">Item 1</div>
<div role="menuitem">Item 2</div>
<div role="menuitem">Item 3</div>
</div>Ensuring Proper Nesting
Ensure that all your menuitem elements are either directly or indirectly (via a child-parent relationship) contained within a menubar or menu element.
Complete Example with Nested Menus:
Here is a more complex example, including nested menus for a drop-down scenario.
Example:
<nav role="menubar">
<div role="menuitem">Home</div>
<div role="menuitem">
About
<div role="menu">
<div role="menuitem">Team</div>
<div role="menuitem">History</div>
</div>
</div>
<div role="menuitem">Contact</div>
</nav>In this example, the main navigation (menubar) contains menuitem elements, and one of those menuitem elements contains a nested menu with additional menuitem elements inside it.
By ensuring your menuitem elements are contained within appropriate parent elements (menubar or menu), you will resolve the W3C HTML Validator issue and improve your web page’s accessibility.
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>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.
A button element cannot contain a descendant element with the attribute tabindex.
The id attribute of an HTML element, used to identify the element when linking, scripting or styling, must be unique in the whole document and must not contain whitespace.
Technically, in HTML5, the value for an id attribute may contain any character, except whitespace characters. However, to avoid inadvertent errors, only ASCII letters, digits, _, and - should be used and the value for an id attribute should start with a letter.