The following notes and warnings highlight missing or conflicting information which caused the validator to perform some guesswork prior to validation, or other things affecting the output below. If the guess or fallback is incorrect, it could make validation results entirely incoherent. It is highly recommended to check these potential issues, and, if necessary, fix them and re-validate the document.
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 (utf-8), for which the parsing mode should be utf-8. However, the document's DOCTYPE Declaration indicates XML mode.
Following the rules of Web Architecture, validation proceeded using the utf-8 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).
Namespace Found in non-XML Document
Namespace "http://www.w3.org/1999/xhtml" found, but the -//W3C//DTD XHTML 1.0 Strict//EN document type is not an XML document type!
Conflict between Mime Type and Document Type
The document is being served with the utf-8 Mime Type which is not a registered media type for the Document Type. The recommended media type for this document is: application/xhtml+xml
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 .mml 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.