HTML Validation

Attribute “isolang” not allowed on element “html” at this point.

About This HTML Issue

Instead of using the isolang attribute to define the language of the document, you can use lang with an ISO 639-1 two character code.

For example, for Portuguese:

<html lang="pt">

Learn more:

→ Wikipedia: list of ISO 639-1 codes

Last reviewed: October 27, 2022

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Related W3C Validator Issues (20)

Bad value “en-EN” for attribute “hreflang” on element “link”: Bad region subtag.

The value en-EN is not a valid language tag for the hreflang attribute on a link element.

The hreflang attribute specifies the language (and optionally, the region) of the linked resource to help search engines and browsers deliver the correct localized version. Language tags should follow BCP 47 standards, with primary language subtags (like en) and optional region subtags (like US). A correct region subtag for English would be en-US (English as used in the United States) or en-GB (United Kingdom). Double language subtags like en-EN are invalid because the region subtag must be a valid country code, not a repeat of the language code.

Correct usage:

<link rel="alternate" href="https://example.com/en/" hreflang="en">
<link rel="alternate" href="https://example.com/en-gb/" hreflang="en-GB">
<link rel="alternate" href="https://example.com/en-us/" hreflang="en-US">

Incorrect usage:

<link rel="alternate" href="https://example.com/en-en/" hreflang="en-EN">

Use en, en-US, or en-GB as appropriate for English-language content, but never en-EN.

Bad value X for attribute “lang” on element “html”: The language subtag X is not a valid ISO language part of a language tag.

Bad value X for attribute “multiple” on element “input”.

Invalid value used for the multiple attribute on an input element.

The multiple attribute is a boolean attribute for certain input types (e.g., email, file). Boolean attributes must appear without a value (or with the same name as value in legacy cases), and they only work on specific types. Valid usage: <input type="email" multiple> or <input type="file" multiple>. Invalid usage includes multiple="1", multiple="true", or using multiple on unsupported types like text or number. The email type allows comma-separated addresses when multiple is present; the file type allows selecting more than one file.

HTML Examples

Example that reproduces the error

<!DOCTYPE html>
<html lang="en">
<head>
  <title>Invalid multiple</title>
</head>
<body>
<!-- Invalid: value on boolean attribute, and wrong type -->

  <input type="text" name="tags" multiple="1">
</body>
</html>

Corrected example

<!DOCTYPE html>
<html lang="en">
<head>
  <title>Valid multiple</title>
</head>
<body>
<!-- Valid: boolean attribute without a value on supported types -->

  <input type="email" name="recipients" multiple placeholder="name@example.com, other@example.com">

  <input type="file" name="attachments" multiple>
</body>
</html>

Consider adding a “lang” attribute to the “html” start tag to declare the language of this document.

lang

HTTP resource not retrievable. The HTTP status from the remote server was: 202.

html
202

HTTP resource not retrievable. The HTTP status from the remote server was: 403.

html
403

HTTP resource not retrievable. The HTTP status from the remote server was: 404.

HTTP resource not retrievable. The HTTP status from the remote server was: 429.

HTTP resource not retrievable. The HTTP status from the remote server was: 503.

html
503

Quirky doctype. Expected “<!DOCTYPE html>”.

doctype
html

The <!DOCTYPE html public "-//W3C//DTD HTML 4.0 Transitional//EN"> doctype triggers quirks mode in modern browsers and is not compliant with HTML5 standards.

The HTML5 specification requires the use of a simple doctype declaration, which ensures standards mode rendering. The correct doctype is <!DOCTYPE html>, which must appear at the very top of every HTML5 document. Legacy doctypes like HTML 4.0 Transitional are obsolete for modern web development and can cause inconsistent browser behavior.

Example of correct usage:

<!DOCTYPE html>
<html lang="en">
  <head>
    <title>Valid HTML5 Doctype Example</title>
  </head>
  <body>
    <p>Your content here.</p>
  </body>
</html>

Replace any legacy or malformed doctype with the above declaration to conform to current HTML standards.

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