Potential Issues

The following missing or conflicting information caused the validator to perform guesswork prior to validation. If the guess or fallback is incorrect, it may make validation results entirely incoherent. It is highly recommended to check these potential issues, and, if necessary, fix them and re-validate the document.

1. Missing "charset" attribute for "" document.

   The HTTP Content-Type header () sent by your web browserserver () did not contain a "charset" parameter, but the Content-Type was one of the XML text/* sub-types.

   The relevant specification (RFC 3023) specifies a strong default of "us-ascii" for such documents so we will use this value regardless of any encoding you may have indicated elsewhere.

   If you would like to use a different encoding, you should arrange to have your browserserver send this new encoding information.

2. No Character Encoding Found!

   Falling back to "" (explain...).

3. Character Encoding Override in effect!

   The detected character encoding "" has been suppressed and "" used instead.

4. No Character Encoding Found! Using Falling back to UTF-8.

   None of the standards sources gave any information on the character encoding labeling for this document. The character encoding UTF-8, which you have chosen via the Encoding override option, will be used for tentative validation.

   None of the standards sources gave any information on the character encoding labeling for this document. Without encoding information it is impossible to reliably validate the document. As a fallback solution, the "UTF-8" encoding was used to read the content and attempt to perform the validation, but this is likely to fail for all non-trivial documents.

   The sources used to find encoding information include:

   • The HTTP Content-Type field.
   • The XML Declaration.
   • The HTML "META" element.

   The algorithm defined in Appendix F of the XML 1.0 Recommendation was also used, without success.

   Since none of these sources yielded any usable information, reliable validation of this document is not possible. Sorry. Please make sure you specify the character encoding in use.

   Specifying a character encoding is typically done by the web server configuration, by the scripts that put together pages, or inside the document itself. IANA maintains the list of official names for character encodings (called charsets in this context). You can choose from a number of encodings, though we recommend UTF-8 as particularly useful.

   The W3C I18N Activity has collected a few tips on how to declare the encoding of a Web document.

   To quickly check whether the document would validate after addressing the missing character encoding information, you can use the "Encoding" form control earlier in the page to force an encoding override to take effect. "iso-8859-1" (Western Europe and North America) and "utf-8" (Universal, but not commonly used in legacy documents) are common encodings if you are not sure what encoding to choose.

   Read the FAQ entry on character encoding for more details and pointers on how to fix this problem with your document.

5. DOCTYPE Override in effect!

   Any DOCTYPE Declaration in the document has been suppressed and the DOCTYPE for "" inserted instead. The document will not be Valid until you alter the source file to reflect this new DOCTYPE.

6. Unable to Determine Parse Mode!

   The validator can process documents either as XML (for document types such as XHTML, SVG, etc.) or SGML (for HTML 4.01 and prior versions). For this document, the information available was not sufficient to determine the parsing mode unambiguously, because:

   • the MIME Media Type () can be used for XML or SGML document types
   • in Direct Input mode, no MIME Media Type is served to the validator
   • the Document Type () is not in the validator's catalog
   • No known Document Type could be detected
   • No XML declaration (e.g <?xml version="1.0"?>) could be found at the beginning of the document.

   As a default, the validator is falling back to SGML mode.

7. Contradictory Parse Modes Detected!

   The validator can process documents either as XML (for document types such as XHTML, SVG, etc.) or SGML (for HTML 4.01 and prior versions).

   This document was served with HTTP headers declaring it as MIME Media Type (), for which the parsing mode should be . However, the document's DOCTYPE Declaration indicates mode.

   Following the rules of Web Architecture, validation proceeded using the mode based on the Content-Type header.

   Fixing this conflict involves either setting the Content-Type header, using a known document type or adding an XML declaration (in the case of XML-based documents).

8. No DOCTYPE found! Attempting validation with .

   The DOCTYPE Declaration was not recognized or is missing. This probably means that the Formal Public Identifier contains a spelling error, or that the Declaration is not using correct syntax. Validation has been performed using a default "fallback" Document Type Definition that closely resembles "", but the document will not be Valid until you have corrected this problem with the DOCTYPE Declaration.

   You should place a DOCTYPE declaration as the very first thing in your HTML document. For example, for a typical XHTML 1.0 document:

         <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
           "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
         <html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en">
           <head>
             <title>Title</title>
           </head>
   
           <body>
             <!-- ... body of document ... -->
           </body>
         </html>
       

   For XML documents, you may also wish to include an "XML Declaration" even before the DOCTYPE Declaration, but this is not well supported in older browsers. More information about this can be found in the XHTML 1.0 Recommendation.

   The W3C QA Activity maintains a List of Valid Doctypes that you can choose from, and the WDG maintains a document on "Choosing a DOCTYPE".

   Learn how to add a doctype to your document from our FAQ.

9. No DOCTYPE found, and unknown root element. Aborting validation.

   The DOCTYPE Declaration was not recognized or is missing. This probably means that the Formal Public Identifier contains a spelling error, or that the Declaration is not using correct syntax, or that your document is not using a DOCTYPE Declaration.

   Without a DOCTYPE Declaration it is not possible to check the validity of your document. Since the document does not start with the root <html> element, automatic fallback to an HTML document type was not performed, and most of the validation process was aborted: only basic markup syntax was checked.

   Learn how to add a doctype to your document from our FAQ, or use the validator's Document Type option to validate your document against a specific Document Type.

10. No DOCTYPE found! Checking XML syntax only.

    The DOCTYPE Declaration was not recognized or is missing. This probably means that the Formal Public Identifier contains a spelling error, or that the Declaration is not using correct syntax, or that your XML document is not using a DOCTYPE Declaration.

    Validation of the document has been skipped, and a simple check of the well-formedness of the XML syntax has been performed instead.

    Learn how to add a doctype to your document from our FAQ, or use the validator's option to validate your XML document against a specific Document Type

11. Unknown Namespace Found

    Unknown namespace "" for document!

12. Namespace Found in non-XML Document

    Namespace "" found, but the document type is not an XML document type!

13. No Namespace Found

    No Namespace was found, but document type requires one to be present!

14. DOCTYPE Override in effect!

    The detected DOCTYPE Declaration "" has been suppressed and the DOCTYPE for "" inserted instead, but even if no errors are shown below the document will not be Valid until you update it to reflect this new DOCTYPE.

15. No DOCTYPE Found!

    Falling back to HTML 4.01 Transitional. (explain...)

16. DOCTYPE Override in effect!

    The DOCTYPE Declaration for "" has been inserted at the start of the document, but even if no errors are shown below the document will not be Valid until you add the new DOCTYPE Declaration.

17. No DOCTYPE Found! Falling Back to .

    A DOCTYPE Declaration is mandatory for most current markup languages and without one it is impossible to reliably validate this document. I am falling back to "" and will attempt to validate the document anyway, but this is very likely to produce spurious error messages for most non-trivial documents.

    The W3C QA Activity maintains a List of Valid Doctypes that you can choose from, and the WDG maintains a document on "Choosing a DOCTYPE".

    So what should I do? Tell me more...

18. No Character Encoding detected!

    To ensure correct validation, processing, and display, it is important that the character encoding is properly labeled. More information...

19. Character Encoding mismatch!

    The character encoding specified in the HTTP header () is different from the value in the XML declaration (). I will use the value from the HTTP header ().

20. Character Encoding mismatch!

    The character encoding specified in the HTTP header () is different from the value in the <meta> element (). I will use the value from the HTTP header () for this validation.

21. Character Encoding mismatch!

    The character encoding specified in the XML declaration () is different from the value in the <meta> element (). I will use the value from the XML declaration () for this validation.

22. Byte-Order Mark found in UTF-8 File.

    The Unicode Byte-Order Mark (BOM) in UTF-8 encoded files is known to cause problems for some text editors and older browsers. You may want to consider avoiding its use until it is better supported.

23. Character Encoding suggestion: use instead of

    The character encoding declared for this document () may not be widely supported. This encoding is equivalent to which may be better supported across platforms.

    More information on declaring a character encoding on your Web server or in your document can be found on the W3C Internationalization site.

24. Conflict between Mime Type and Document Type

    The document is being served with the Mime Type which is not a registered media type for the Document Type. The recommended media type for this document is:

    Using a wrong media type for a certain document type may confuse the validator and other user agents with respect to the nature of the document, and you may get some erroneous validation errors. How to fix this problem? One of the following techniques should help:

    • If you are serving a static file on a Web server, changing its extension should help. Use e.g .xhtml for XHTML or .mathml for MathML.
    • You may need to reconfigure your Web server. This Setting up MIME Types tutorial has instructions for Apache, Tomcat and IIS.
    • If the document is generated dynamically, the scripting language should allow you to set up the mime type: this article on MIME Types and Content Negotiation has examples in PHP, Perl, and ASP.

25. Rare or unregistered character encoding detected

    The character encoding declared for this document () is supported by the validator, but may not be widely supported across platforms. For the sake of interoperability, it is best to use a unicode character encoding such as UTF-8, or one of the registered character encodings.

    More information on declaring a character encoding on your Web server or in your document can be found on the W3C Internationalization site.

26. document without DOCTYPE detected.

    This document does not declare any DOCTYPE. A Doctype declaration is generally needed for validation, but the checked document uses markup specific to , which may be used without DOCTYPE.

    Validation was performed as if the DOCTYPE for was present. If this automatic detection is not correct, adding a DOCTYPE declaration will help validate without ambiguity.