HTML Guide

A “meta” element with an “http-equiv” attribute whose value is “X-UA-Compatible” must have a “content” attribute with the value “IE=edge”.

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.

Learn more:

Related W3C validator issues

A document must not include both a “meta” element with an “http-equiv” attribute whose value is “content-type”, and a “meta” element with a “charset” attribute.

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">

Attribute “http-equiv” not allowed on element “meta” at this point.

A <meta> element using the http-equiv attribute has been found in an unexpected place of the document. It should appear inside the <head> section, like in this example:

<!DOCTYPE html>
<html lang="">
  <head>
    <meta http-equiv="content-type" content="text/html; charset=UTF-8">
    <title>Test</title>
  </head>
  <body>
    <p>Content of the page</p>
  </body>
</html>

The http-equiv attribute is used in web pages to simulate an HTTP response header. While HTTP response headers can be set from the server, not everyone has access to the server configuration, so an alternative is using <meta http-equiv> to define settings that would otherwise require setting an HTTP response header.

The most popular use of http-equiv are defining the content-type of the document as in the example above, although in HTML5 it’s preferred to use this instead:

<meta charset="UTF-8">

Another popular use of the http-equiv is setting an automatic reload of the web page, for example this will have the browser reload the page every 60 seconds:

<meta http-equiv="refresh" content="60">

However, refreshing a page automatically is a bad practice regarding accessibility, as users do not expect a page to do that, and doing so will move focus back to the top of the page, which may create a frustrating or confusing experience.

Other values that can be used with the http-equiv attribute include:

content-security-policy
content-length.
content-encoding
default-style
window-target

Bad value “Cache-Control” for attribute “http-equiv” on element “meta”.

The value “Cache-Control” is not valid for the http-equiv attribute in a meta tag.

The http-equiv attribute in the meta tag is used to define HTTP header equivalents, and it has specific valid values, such as “content-type”, “expires”, “refresh”, and “content-security-policy”. Most commonly used values are defined in the HTML specifications.

To resolve this issue, you must remove or correct the http-equiv attribute value. If controlling cache behavior is necessary, it should be handled via server configuration rather than within the HTML document using a meta tag.

Example

Incorrect usage:

<!DOCTYPE html>
<html lang="en">
<head>
  <meta http-equiv="Cache-Control" content="no-cache">
</head>
<body>
  <p>Sample text on the page.</p>
</body>
</html>

Corrected version (removing the invalid meta tag):

<!DOCTYPE html>
<html lang="en">
<head>
  <!-- Cache-Control should be configured on the server-side -->
</head>
<body>
  <p>Sample text on the page.</p>
</body>
</html>

You might configure caching on your web server (e.g., Apache, Nginx) to handle Cache-Control instead of using an invalid meta tag in your HTML.

Bad value “cleartype” for attribute “http-equiv” on element “meta”.

Bad value “Content-Script-Type” for attribute “http-equiv” on element “meta”.

Bad value “”Content-Security-Policy”” for attribute “http-equiv” on element “meta”.

The W3C HTML Validator issue you’re encountering indicates that the value specified for the http-equiv attribute in a <meta> tag is not valid. This often happens due to incorrect formatting, spelling errors, or extraneous characters in the attribute value.

To resolve this issue, ensure that the http-equiv attribute is spelled correctly and that it contains valid values. For a basic Content Security Policy (CSP), the correct way to specify it in the <meta> tag is as follows:

Correct Usage of <meta> with http-equiv

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="Content-Security-Policy" content="default-src 'self';">
    <title>Document Example</title>
</head>
<body>
    <h1>Hello, World!</h1>
</body>
</html>

Fixes to Apply:

Ensure Correct Spelling: The attribute value must be spelled exactly as “Content-Security-Policy” (case-sensitive).
Check for Extraneous Characters: Make sure there are no extra quotes or spaces within the attribute value.

Example of a Bad Value:

If your original <meta> tag looks something like this:

<meta http-equiv=""Content-Security-Policy"" content="default-src 'self';">

You should change it to:

<meta http-equiv="Content-Security-Policy" content="default-src 'self';">

Bad value “Content-Style-Type” for attribute “http-equiv” on element “meta”.

Bad value “Expires” for attribute “http-equiv” on element “meta”.

Expires is not a valid value for the http-equiv attribute in HTML5.

The http-equiv attribute is used with the <meta> tag to configure the HTTP headers of the web page. In HTML5, the allowed values for http-equiv include content-type, default-style, refresh, and security-related headers like Content-Security-Policy. The Expires header is an HTTP header typically set in server configurations or via server-side scripting, not through HTML. To control page caching, consider using server-side headers for Expires or use the cache-control setting if supported by your server.

Here’s how you might correct an HTML document using valid http-equiv values and manage caching through server-side configurations:

Example of Valid HTML <meta> Tags:

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <title>Example Page</title>
</head>
<body>
  <h1>Welcome to My Website</h1>
</body>
</html>

Example of Setting Expires at Server Level:

If you’re using Apache, you might set Expires in a .htaccess file:

<IfModule mod_expires.c>
  ExpiresActive On
  ExpiresByType text/html "access plus 1 week"
</IfModule>

For Nginx, such settings would be in the server’s configuration file:

location ~* \.html$ {
  expires 7d;
}

Using these methods, you ensure compliance with HTML5 standards by handling HTTP headers correctly.

Bad value “Pragma” for attribute “http-equiv” on element “meta”.

Pragma is not a valid value for the http-equiv attribute in HTML5.

In HTML5 (as defined by the WHATWG living standard and W3C), the http-equiv attribute on the meta element only allows certain tokens, such as content-type, default-style, and refresh. The use of Pragma is obsolete and was mainly supported in older HTML specifications for compatibility with HTTP/1.0 proxies. The recommended way to control caching in modern web development is through appropriate HTTP headers sent from the server.

Example of the incorrect usage:

<meta http-equiv="Pragma" content="no-cache">

Correct usage for controlling cache with HTML meta tags (but note, affects only some browsers and is not reliable):

<meta http-equiv="Cache-Control" content="no-cache">

However, even Cache-Control in a meta tag has limited effectiveness. The best practice is to set Cache-Control and Pragma headers server-side, not in HTML.

Correct server-side (not HTML) example:

Cache-Control: no-cache
Pragma: no-cache

Summary:
Remove the <meta http-equiv="Pragma" content="no-cache"> tag from your HTML and rely on server-side HTTP headers to manage caching. If you still need a meta-based (less effective) solution for rare cases, use http-equiv="Cache-Control".

Minimal valid HTML example (without the invalid meta tag):

<!DOCTYPE html>
<html lang="en">
  <head>
    <title>No Invalid http-equiv Value</title>
  </head>
  <body>
    <!-- Content goes here -->
  </body>
</html>

Element “meta” is missing one or more of the following attributes: “charset”, “content”, “http-equiv”, “itemprop”, “name”, “property”.

There’s an incomplete or incorrectly formed <meta> tag. The <meta> tag in HTML is used to provide metadata about the HTML document. This metadata is typically specified using attributes like charset, content, http-equiv, itemprop, name, and property.

To fix this issue, you need to ensure that your <meta> tags include at least one of these attributes. Here are some examples of properly formed <meta> tags with each of these attributes:

Using the charset attribute:
```
<meta charset="UTF-8">
```
This specifies the character encoding for the HTML document, which is crucial for displaying text correctly in different languages.
Using the content and name attributes:
```
<meta name="description" content="A brief description of the webpage content.">
```
This provides a description of the webpage content, which can be used by search engines.
Using the http-equiv and content attributes:
```
<meta http-equiv="refresh" content="30">
```
This specifies information to be passed to the browser, such as refreshing the page every 30 seconds.
Using the property and content attributes:
```
<meta property="og:title" content="Your Webpage Title">
```
This is used for Open Graph meta tags, which improve the appearance of shared content on social media platforms.

Correct Usage Example

Here’s an example of an HTML document with a properly formed set of <meta> tags:

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta name="description" content="A brief description of the webpage content.">
    <meta http-equiv="refresh" content="30">
    <meta property="og:title" content="Your Webpage Title">
    <title>Document</title>
</head>
<body>
    <!-- Page content goes here -->
</body>
</html>