Description of Errors

HTML5 Character Encoding Errors

Character encoding $0 is not allowed for HTML document.

The character encoding used for the document is not allowed for HTML document. The document is non‐conforming.

 Character encoding $0 should not be used for HTML document.

The character encoding used for the document is not recommended for HTML document. The document is non‐conforming unless there is any good reason to use that encoding.

 Use of UTF-8 is encouraged.

Use of UTF-8 as the character encoding of the document is encouraged, though the use of another character encoding is conforming.

 Conformance for character encoding requirements cannot be checked.

The conformance checker cannot detect whether the input document met the requirements on character encoding, since the document is not inputed as a serialized byte sequence. The document is not conforming if it is not encoded in an appropriate character encoding with appropriate labeling.

 There is no character encoding declaration.

The document does not contain a character encoding declaration. Unless the character encoding is explicitly specified in lower‐level protocol, e.g. in HTTP, or is implied by BOM, there must be a character encoding declaration. The document is non‐conforming.

The long character encoding declaration syntax <meta http-equiv="Content-Type" content="text/html; charset=charset-name"> is obsolete. The new syntax is:

<meta charset="charset-name">

Note that the encoding declaration in XML declaration has no effect for HTML document.

 No character encoding metadata is found in lower‐level protocol nor is there BOM, while character encoding $0 is not a superset of ASCII.

The document is not labeled with character encoding name in lower‐level protocol, e.g. in HTTP, and the document is not begin with BOM. In addition, the character encoding of the document is not a superset of ASCII. The document is non‐conforming.

Unless there is a BOM, the character encoding for the document must be specified in e.g. HTTP‐level, as:

Content-Type: text/html; charset=charset-name

Existence of HTML character encoding declaration, i.e. <meta charset="charset-name">, does not allow to omit charset parameter for HTML document encoded in non‐ASCII compatible encoding.

Character encodings Shift_JIS, Windows-31J, and ISO-2022-JP are not a superset of ASCII for the purpose of HTML conformance.

 While parsing the document as $0, a character encoding declaration specifying character encoding as $1 is found. The document is reparsed.

While parsing a document in a character encoding, a character encoding declaration which declares the character encoding of the document as another character encoding is found. The occurence of this warning itself does not make the document non‐conforming. However, the failure of the first attempt to to detect the character encoding might be the result of non‐conformance of the document.

The document will be reparsed from the beginning. Some error or warning might be reported again.

These are suggestions to avoid this warning:

  • Specify charset parameter in the Content-Type field in the HTTP header, as: 
    Content-Type: text/html; charset="charset-name"
  • Put the character encoding declaration (<meta charset="charset-name">) just after <head> start tag.
  • Use UTF-8.

HTML5 Parse Errors in Tokenization Stage

Tag <$0> is not allowed after the end tag </html>.

The start or end tag of an element appears after the html element has been closed. The document is non-conforming.

Any content of the document other than comments must be put into the html element.

 Tag <$0> is not allowed after the end tag </body>.

The start or end tag of an element appears after the body element has been closed. The document is non-conforming.

Any content of the document other than head contents and comments must be put into the body element.

 The & character must introduce a reference.

An & character which is not part of any reference appears in the input stream. The document is non‐conforming.

Any & character in URI (or IRI) must be escaped as &amp;.

The & character must be the first character of a reference:

Named entity reference
&entity-name;
where entity-name is the name of the