Notes and Potential Issues
The following notes and warnings highlight missing or conflicting information which caused the validator to perform some guesswork prior to validation. 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.
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 (text/html) can be used for XML or SGML document types
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.
No XML namespace (e.g <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">) could be found at the root of the document.
As a default, the validator is falling back to SGML mode.
No Character encoding declared at document level
No character encoding information was found within the document, either in an HTML meta element or an XML declaration. It is often recommended to declare the character encoding in the document itself, especially if there is a chance that the document will be read from or saved to disk, CD, etc.