test/html-webhacc/error-description-source.xml

<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml"
    xmlns:d="http://suika.fam.cx/~wakaba/archive/2007/wdcc-desc/"
    id="error-description">
<head>
<base href="cc/"/>
<title xml:lang="en">Description of Errors &#x2014; WebHACC (β)</title>
<title xml:lang="ja">誤りの説明 &#x2014; WebHACC (β)</title>
<link rel="stylesheet" href="../cc-style"/>
<link rel="license" href="#license"/>
</head>
<body>
<header>
<h1><a href="../cc-about"><abbr title="Web Hypertext Application Conformance Checker (β)"><img src="../icons/title" alt="WebHACC"/></abbr></a></h1>
<h2>Description of Errors</h2>
</header>

<d:cat name="WebHACC:Title">
  <d:text xml:lang="en">WebHACC (β)</d:text>
</d:cat>

<d:cat name="WebHACC:Heading">
  <d:text xml:lang="en">
    <a href="../error-description#WebHACC:Heading" rel="help"><abbr title="Web Hypertext Application Conformance Checker (β)"><img src="../icons/title" alt="WebHACC"/></abbr></a>
  </d:text>
  <d:text xml:lang="ja">
    <a href="../error-description#WebHACC:Heading" rel="help"><abbr title="Web ハイパーテキスト応用適合性検査器 (β)"><img src="../icons/title" alt="WebHACC"/></abbr></a>
  </d:text>
  <d:desc xml:lang="en">
    <p><a href="./#input"><abbr title="Web Hypertext Application Conformance Checker">WebHACC</abbr></a>
    is a <em>conformance checker</em> (or validator) for Web documents,
    supporting <a href="../standards">latest Web standards</a> including
    <a href="http://whatwg.org/html5"><abbr title="Hypertext Markup Language">HTML</abbr>5</a>,
    <a href="urn:ietf:rfc:4287">Atom 1.0</a>,
    <a href="http://www.w3.org/Style/CSS/current-work"><abbr title="Cascading Style Sheets">CSS</abbr>3</a>.</p>

    <p><strong><a href="./#input">Check your document</a></strong>, or
    <a href="../cc-about">learn more about
    <abbr title="Web Hypertext Application Conformance Checker">WebHACC</abbr></a>.</p>
  </d:desc>
  <d:desc xml:lang="ja">
    <p><a href="./#input"><abbr title="Web ハイパーテキスト応用適合性検査器">WebHACC</abbr></a>
    は、 Web 文書のための<em>適合性検査器</em> (妥当性検証器) です。
    <a href="http://whatwg.org/html5"><abbr title="Hypertext Markup Language">HTML</abbr>5</a>、
    <a href="urn:ietf:rfc:4287">Atom 1.0</a>、
    <a href="http://www.w3.org/Style/CSS/current-work"><abbr title="Cascading Style Sheets">CSS</abbr>3</a>
    などの<a href="../standards">最新の Web 標準</a>に対応しています。</p>

    <p><strong><a href="./#input">文書を検査する</a></strong></p>

    <p><a href="../cc-about"><abbr title="Web ハイパーテキスト応用適合性検査器">WebHACC</abbr>
    の詳細</a></p>
  </d:desc>
</d:cat>

<section id="character-encoding-layer">
<h2>Character Encoding Layer Errors</h2>

<d:item name="fallback-char-error"
    modules="Charset::DecodeHandle">
  <d:message xml:lang="en">Octet sequence <code><var>{octets}</var></code>
  is not an allowed representation of the character
  <code><var>{char}</var></code> &#x2014; character reference
  <code><var>{char:hexref}</var></code> should be used instead.</d:message>
  <!-- HTML5 parse error -->
</d:item>

<d:item name="fallback-unassigned-error"
    modules="Charset::DecodeHandle">
  <d:message xml:lang="en">No character is assigned to octet sequence
  <code><var>{octets}</var></code>.</d:message>
  <!-- HTML5 parse error -->
</d:item>

<d:item name="illegal-octets-error"
    modules="Charset::DecodeHandle">
  <d:message xml:lang="en">Octet sequence <code><var>{octets}</var></code>
  is illegal.</d:message>
</d:item>

<d:item name="invalid-state-error"
    modules="Charset::DecodeHandle::ISO2022JP">
  <!-- TODO: more user-friendly error message is desired... -->
  <d:message xml:lang="en">The input stream is broken.</d:message>
  <d:desc xml:lang="en">
    <p>The input stream is encoded in <code>ISO-2022-JP</code>
    or its variant but is partially broken.</p>

    <p>Note that an <code>ISO-2022-JP</code> stream must end in the ASCII
    state.</p>
  </d:desc>
</d:item>

<d:item name="unassigned-code-point-error"
    modules="Charset::DecodeHandle">
  <d:message xml:lang="en">No character is assigned to octet sequence
  <code><var>{octets}</var></code>.</d:message>
</d:item>
</section>

<section id="html5-character-encoding">
<h2>HTML5 Character Encoding Errors</h2>

<d:item name="disallowed character encoding"
    modules="ContentChecker">
  <d:message xml:lang="en">Character encoding <code><var>{text}</var></code>
  is not allowed for <abbr>HTML</abbr> document.</d:message>
  <d:desc xml:lang="en">
    <p>The character encoding used for the document is not allowed
    for <abbr>HTML</abbr> document.  The document is non‐conforming.</p>
  </d:desc>
</d:item>

<d:item name="bad character encoding"
    modules="ContentChecker">
  <d:message xml:lang="en">Character encoding <code><var>{text}</var></code>
  should not be used for <abbr>HTML</abbr> document.</d:message>
  <d:desc xml:lang="en">
    <p>The character encoding used for the document is not recommended
    for <abbr>HTML</abbr> document.  The document is non‐conforming
    unless there is any good reason to use that encoding.</p>
  </d:desc>
</d:item>

<d:item name="non-utf-8 character encoding"
    modules="ContentChecker">
  <d:message xml:lang="en">Use of UTF-8 is encouraged (this document
  is encoded in <code><var>{text}</var></code>).</d:message>
  <d:desc xml:lang="en">
    <p>Use of UTF-8 as the character encoding of the document is encouraged,
    though the use of another character encoding is still conforming.</p>
  </d:desc>
</d:item>

<d:item name="character encoding unchecked"
    modules="ContentChecker">
  <d:message xml:lang="en">Conformance for character encoding requirements
  cannot be checked, since the input is not a byte stream.</d:message>
  <d:desc xml:lang="en">
    <p>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.</p>
  </d:desc>
</d:item>

<d:item name="no character encoding declaration"
    modules="ContentChecker">
  <d:message xml:lang="en">There is no character encoding
  declaration.</d:message>
  <d:desc xml:lang="en">
    <p>The document does not contain a character encoding 
    declaration.  Unless the character encoding is explicitly 
    specified in lower‐level protocol, e.g. in <abbr>HTTP</abbr>,
    or is implied by <abbr>BOM</abbr>, there must be a character
    encoding declaration.  The document is non‐conforming.</p>

    <p>The long character encoding declaration syntax
    <code class="html bad example">&lt;meta http-equiv="Content-Type" content="text/html; charset=<var>charset-name</var>"></code>
    is obsolete.  The new syntax is:</p>
    <pre class="html example"><code>&lt;meta charset="<var>charset-name</var>"></code></pre>

    <p>Note that the <code>encoding</code> declaration in <abbr>XML</abbr> 
    declaration has no effect for <abbr>HTML</abbr> document.</p>
  </d:desc>
</d:item>

<d:item name="non ascii superset"
    modules="ContentChecker">
  <d:message xml:lang="en">No character encoding metadata is found
  in lower‐level protocol nor is there <abbr>BOM</abbr>, while
  character encoding <code><var>{text}</var></code>
  is not a superset of <abbr>ASCII</abbr>.</d:message>
  <d:desc xml:lang="en">
    <p>The document is not labeled with character encoding name
    in lower‐level protocol, e.g. in <abbr>HTTP</abbr>, and
    the document is not begin with <abbr>BOM</abbr>.  In addition,
    the character encoding of the document is not a superset of
    <abbr>ASCII</abbr>.  The document is non‐conforming.</p>

    <p>Unless there is a <abbr>BOM</abbr>, the character encoding
    for the document must be specified in e.g. <abbr>HTTP</abbr>‐level,
    as:</p>
    <pre class="http example"><code>Content-Type: text/html; charset=<var>charset-name</var></code></pre>

    <p>Existence of <abbr>HTML</abbr> character encoding declaration, i.e.
    <code class="html example">&lt;meta charset="<var>charset-name</var>"></code>,
    does not allow to omit <code>charset</code> parameter
    for <abbr>HTML</abbr> document encoded in non‐<abbr>ASCII</abbr>
    compatible encoding.</p>

    <p>Character encodings <code>Shift_JIS</code>, <code>Windows-31J</code>,
    and <code>ISO-2022-JP</code> are <em>not</em> a superset of
    <abbr>ASCII</abbr> for the purpose of <abbr>HTML</abbr> conformance.</p>
  </d:desc>
</d:item>

<d:item name="sniffing:chardet"
    modules="HTML::Parser">
  <d:message xml:lang="en">Character encoding of this document is sniffed
  as <code><var>{text}</var></code> (Sniffed because no explicit specification
  for the character encoding of this document is found in the transfer
  procotol headers).</d:message>
</d:item>

<d:item name="sniffing:default"
    modules="HTML::Parser">
  <d:message xml:lang="en">Character encoding of this document is defaulted
  to <code><var>{text}</var></code> because no explicit specification
  for the character encoding of this document is found in the transfer
  procotol headers.</d:message>
</d:item>

<d:item name="chardecode:fallback"
    modules="HTML::Parser">
  <d:message xml:lang="en">Results might be <em>wrong</em>, since the
  conformance checker cannot find an appropriate decoder for the character
  encoding used for the document.</d:message>
  <d:desc xml:lang="en">
    <p>The conformance checker cannot find an appropriate decoder for
    the character encoding used to encode characters in the document.</p>

    <p>This error is raised if:</p>
    <ul>
    <li>the conformance checker cannot find any decoder for the character
    encoding in use, but it knows that the encoding is similar to another
    character encoding, such that it uses the decoder for that character
    encoding, and therefore some octets might be interpreted incorrectly,
    or,</li>
    <li>the conformance checker find a decoder for the character encoding
    in use, but it does not know whether the decoder is conforming to the
    relevant specification or not, and therefore some octets might be
    interpreted incorrectly.</li>
    </ul>

    <p>In either case, the result shown by the conformance checker might
    contain wrong errors caused by errorneous decoder or might not contain 
    errors that should be raised if an appropriate decoder is used.</p>

    <!-- TODO: add advise that either install relevant modules or 
         join the developmenet of the modules... -->
  </d:desc>
</d:item>

<d:item name="chardecode:no error"
    modules="HTML::Parser">
  <d:message xml:lang="en">Conformance error checking for the character
  encoding <code><var>{text}</var></code> is not supported.</d:message>
</d:item>

<d:item name="charset label:matching"
    modules="HTML::Parser">
  <d:message xml:lang="en">Sniffed character encoding 
  <code><var>{text}</var></code> is same as the character encoding specified
  in the character encoding declaration.  This is <em>not</em> an
  error.</d:message>
</d:item>

<d:item name="charset label detected"
    modules="HTML::Parser">
  <d:message xml:lang="en">While parsing the document as
  <code><var>{text}</var></code>, a character encoding declaration specifying
  a different character encoding is found.  The document
  is reparsed.</d:message>
  <d:desc xml:lang="en">
    <p>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 a result of non‐conformance 
    of the document.</p>

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

    <p>These are suggestions to avoid this warning:</p>
    <ul>
    <li>Specify <code>charset</code> parameter in the <code>Content-Type</code>
    field in the <abbr>HTTP</abbr> header, as:
    <pre class="HTTP example"><code>Content-Type: text/html; charset="<var>charset-name</var>"</code></pre></li>
    <li>Put the character encoding declaration
    (<code class="html example">&lt;meta charset="<var>charset-name</var>"></code>)
    just after <code class="html example">&lt;head></code> start tag.</li>
    <li>Use <code>UTF-8</code>.</li>
    </ul>
  </d:desc>
</d:item>

<d:item name="NULL"
    modules="HTML::Parser">
  <d:message xml:lang="en">The <code class="charname">NULL</code> character
  is not allowed.</d:message>
</d:item>

<d:item name="control char"
    modules="HTML::Parser">
  <d:message xml:lang="en">Code point <code><var>{text}</var></code> is
  not allowed.</d:message>
</d:item>

</section>

<section id="html5-tokenize-error">
<h2>HTML5 Parse Errors in Tokenization Stage</h2>

<d:item name="bad attribute name"
    modules="HTML::Parser">
  <d:message xml:lang="en">Attribute name cannot contain characters
  <code>"</code>, <code>'</code>, and <code>=</code>.</d:message>
</d:item>

<d:item name="bad attribute value"
    modules="HTML::Parser">
  <d:message xml:lang="en">Attribute value must be quoted by <code>"</code>
  or <code>'</code> if it contains a <code>"</code>, <code>'</code>, or
  <code>=</code> character.</d:message>
  <d:desc xml:lang="en">
    <p>In an unquoted attribute value, a character <code>"</code>
    (<code>U+0022</code> <code class="charname">QUOTATION MARK</code>),
    <code>'</code> (<code>U+0026</code> 
    <code class="charname">APOSTROPHE</code>), or <code>=</code>
    (<code>U+003D</code> <code class="charname">EQUAL SIGN</code>)
    is contained.  These characters are not allowed in unquoted attribute
    values, since they are used to quote attribute values or to separate
    attribute name and value.</p>

    <p>This error is also raised if one try to use empty attribute
    value like <code class="html bad example">&lt;foo bar= baz=></code>;
    in this example, <code class="html bad example">baz=</code> is
    treated as an invalid attribute value for the attribute
    <code class="html bad example">bar</code>, not as another attribute.</p>
  </d:desc>
</d:item>

<d:item name="bare ero"
    modules="HTML::Parser">
  <d:message xml:lang="en">The <code>&amp;</code> character must
  be escaped as <code class="html example">&amp;amp;</code>.</d:message>
  <d:desc xml:lang="en">
    <p>An <code>&amp;</code> character which
    is not part of any reference appears in the input stream.
    The document is non‐conforming.</p>

    <p><em>Any <code>&amp;</code> character in URI (or IRI)
    must be escaped as <code class="example">&amp;amp;</code>.</em></p>

    <p>The <code>&amp;</code> character must
    be the first character of a reference:
      <dl class="switch">
      <dt>Named entity reference</dt>
          <dd><pre class="html example"><code>&amp;<var>entity-name</var>;</code></pre>
          where <var>entity-name</var> is the name of the
          character entity to be referenced.</dd>
      <dt>Numeric character reference</dt>
          <dd><pre class="html example"><code>&amp;#<var>d</var>;</code></pre>
          where <var>d</var> is the decimal representation of
          the code position of the character to be referenced.</dd>
      <dt>Hexadecimal character reference</dt>
          <dd><pre class="html example"><code>&amp;#x<var>h</var>;</code></pre>
          where <var>h</var> is the hexadecimal representation
          of the code position of the character to be referenced.</dd>
      </dl>
    </p>

    <p>To represent <code>&amp;</code> as a data character, use
    named entity reference:
      <pre class="html example"><code>&amp;amp;</code></pre>
    </p>
  </d:desc>
</d:item>

<d:item name="bare etago"
    modules="HTML::Parser">
  <d:message xml:lang="en">A <code>&lt;/</code> string is not followed
  by a tag name.</d:message><!-- </ EOF -->
  <d:desc xml:lang="en">
    <p>There is a <code>&lt;</code> (<code>U+003C</code> 
    <code class="charname">LESS-THAN SIGN</code>) character
    immediately followed by a <code>/</code> (<code>U+005F</code>
    <code>SOLIDUS</code>) character, which is not part
    of any end tag, in the input stream.  The document
    is non-conforming.</p>

    <p>The <code>&lt;/</code> sequence immediately followed
    by an <abbr title="End of file pseudo-character">EOF</abbr> is
    interpreted as a string data of <code>&lt;/</code>.</p>

    <p>The <code>&lt;/</code> sequence as string data must
    be escaped as:
    <pre class="html example"><code>&amp;lt;/</code></pre>
    </p>
  </d:desc>
</d:item>

<d:item name="bare stago"
    modules="HTML::Parser">
  <d:message xml:lang="en">A <code>&lt;</code> character is not followed
  by tag name or by a <code>!</code> character.</d:message>
  <d:desc xml:lang="en">
    <p>A <code>&lt;</code> (<code>U+003C</code> 
    <code class="charname">LESS-THAN SIGN</code>) character which is not part
    of any markup appears in the input stream.</p>

    <p>The <code>&lt;</code> character as a data character must
    be escaped as:
    <pre class="html example"><code>&amp;lt;</code></pre>
    </p>
  </d:desc>
</d:item>

<d:item name="bare nero"
    modules="HTML::Parser">
  <d:message xml:lang="en">The decimal representation of the code position
  of a character must be specified after <code>&amp;#</code>.</d:message>
  <d:desc xml:lang="en">
    <p>An <code>&amp;</code> (<code>U+0026</code>
    <code class="charname">AMPERSAND</code>) character immediately
    followed by a <code>#</code> (<code>U+0023</code>
    <code>NUMBER SIGN</code>) character which
    is not part of any reference appears in the input stream.
    The document is non-conforming.</p>

    <p>The string <code>&amp;#</code> must be the first two characters
    of a reference:
      <dl class="switch">
      <dt>Numeric character reference</dt>
          <dd><pre class="html example"><code>&amp;#<var>d</var>;</code></pre>
          where <var>d</var> is the decimal representation of
          the code point of the character to be referenced.</dd>
      <dt>Hexadecimal character reference</dt>
          <dd><pre class="html example"><code>&amp;#x<var>h</var>;</code></pre>
          where <var>h</var> is the hexadecimal representation
          of the code point of the character to be referenced.</dd>
      </dl>
    </p>

    <p>To represent <code>&amp;#</code> as data characters, use
    a named entity reference for the <code>&amp;</code> character:
      <pre class="html example"><code>&amp;amp;#</code></pre>
    </p>
  </d:desc>
</d:item>

<d:item name="bare hcro"
    modules="HTML::Parser">
  <d:message xml:lang="en">The hexadecimal representation of the code position
  of a character must be specified after <code>&amp;#x</code>.</d:message>
  <d:desc xml:lang="en">
   <p>The string <code>&amp;#x</code> or <code>&amp;#X</code> which
   is not part of any reference appears in the input stream.
    The document is non-conforming.</p>

    <p>The string <code>&amp;#x</code> or <code>&amp;#X</code> must
    be the first three characters of a hexadecimal reference:
      <pre class="html example"><code>&amp;#x<var>h</var>;</code></pre>
    where <var>h</var> is the hexadecimal representation
    of the code point of the character to be referenced.</p>

    <p>To represent <code>&amp;#x</code> as data characters, use
    a named entity reference for the <code>&amp;</code> character:
      <pre class="html example"><code>&amp;amp;#x</code></pre>
    </p>
  </d:desc>
</d:item>

<d:item name="bogus comment"
    modules="HTML::Parser">
  <d:message xml:lang="en">String <code>&lt;!</code> is not followed
  by <code>--</code>.</d:message>
  <d:desc xml:lang="en">
    <p>There is a <code>&lt;</code> (<code>U+003C</code> 
    <code class="charname">LESS-THAN SIGN</code>) character
    followed by a <code>!</code> (<code>U+0021</code>
    <code class="charname">EXCLAMATION MARK</code>) character,
    which is not followed by a <code>--</code> or
    <code>!DOCTYPE</code>.  The document is non-conforming.</p>

    <dl class="switch">
    <dt>Comments</dt>
      <dd>In HTML document, comments must be introduced by
      <code class="example">&lt;!--</code> (<code>&lt;!</code>
      <em>immediately</em> followed
      by <em>two</em> <code>-</code>s) and must be terminated by
      <code class="example">--></code>.
      Strings <code>&lt;!</code> not followed
      by <code>--</code> and <code>&lt;!-</code> not followed by
      <code>-</code> are not valid open delimiters for comments.</dd>
    <dt>Marked sections, including <code>CDATA</code> sections</dt>
      <dd>Marked sections are not allowed in HTML document.</dd>
    <dt>Markup declarations</dt>
      <dd>Markup declarations, except for <code>DOCTYPE</code>
      and comment declarations, are not allowed in HTML document.</dd>
    <dt>String <code>&lt;!</code></dt>
      <dd>String <code>&lt;!</code> must be escaped as
      <code class="example">&amp;lt;!</code>.</dd>
    </dl>
  </d:desc>
</d:item>

<d:item name="bogus end tag"
    modules="HTML::Parser">
  <d:message xml:lang="en">String <code>&lt;/</code> is not followed
  by tag name.</d:message><!-- </ non-name-start-char-non-EOF -->
  <d:desc xml:lang="en">
    <p>There is a <code>&lt;</code> (<code>U+003C</code> 
    <code class="charname">LESS-THAN SIGN</code>) character
    immediately followed by a <code>/</code> (<code>U+005F</code>
    <code>SOLIDUS</code>) character, which is not part
    of any end tag, in the input stream.  The document
    is non-conforming.</p>

    <p>The <code>&lt;/</code> sequence not followed by a
    tag name is parsed as an opening of bogus comment.</p>

    <p>The <code>&lt;/</code> sequence as string data must
    be escaped as:
    <pre class="html example"><code>&amp;lt;/</code></pre>
    </p>
  </d:desc>
</d:item>

<d:item name="C1 character reference"
    modules="HTML::Parser">
  <d:message xml:lang="en">Character reference to
  <code><var>{text}</var></code> is not allowed.</d:message>
</d:item>

<d:item name="CR character reference"
    modules="HTML::Parser">
  <d:message xml:lang="en">Character reference to
  <code>U+000D</code> (<code class="charname">CARRIAGE RETURN</code>)
  is not allowed.</d:message>
</d:item>

<d:item name="dash in comment"
    modules="HTML::Parser">
  <d:message xml:lang="en">There is a <code>--</code> sequence
  in a comment.</d:message>
  <d:desc xml:lang="en">
    <p>There is a <code>-</code> (<code>U+002D</code>
    <code class="charname">HYPHEN-MINUS</code>) character 
    at the end of the comment or a <code>--</code> sequence
    in the comment.  The document is non-conforming.</p>

    <p>Comments cannot contain a string <code>--</code>, as in XML.
    Unlike SGML, there cannot be more than one comments
    (where <i>comment</i> is an SGML term) in the comment
    declaration.</p>
  </d:desc>
</d:item>

<d:item name="duplicate attribute"
    modules="HTML::Parser">
  <d:message xml:lang="en">There are two attributes with name
      <code><var>{text}</var></code>.</d:message>
  <d:desc xml:lang="en">
    <p>There are more than one attributes with the same
    name in a tag.  The document is non-conforming.</p>

    <p>The <code>motion</code> attribute is not part of the HTML standard.
    Use <code>img</code> element with animation GIF instead.</p>
  </d:desc>
</d:item>

<d:item name="empty start tag"
    modules="HTML::Parser">
  <d:message xml:lang="en">Empty start tag (<code>&lt;></code>) is not
  allowed.</d:message>
</d:item>

<d:item name="empty end tag"
    modules="HTML::Parser">
  <d:message xml:lang="en">Empty end tag (<code>&lt;/></code>) is not
  allowed.</d:message>
</d:item>

<d:item name="end tag attribute"
    modules="HTML::Parser">
  <d:message xml:lang="en">End tag cannot have attributes.</d:message>
  <d:message xml:lang="ja">終了タグに属性が指定されています。</d:message>
</d:item>

<d:item name="empty unquoted attribute value"
    modules="HTML::Parser">
  <d:message xml:lang="en">Attribute value is not specified.</d:message>
  <d:message xml:lang="ja">属性値が指定されていません。</d:message>
  <d:desc xml:lang="en">
    <p>The attribute value is not specified after the <code>=</code>
    (<code>U+003C</code> <code class="charname">EQUAL SIGN</code>)
    character.</p>

    <p>When an attribute value is empty, the <code>=</code> character after
    the attribute name must be specified as:</p>

    <p><code class="html example">&lt;foo bar></code></p>

    <p>Instead, quotation marks can be used to explicitly represent that
    the attribute value is empty, as:</p>

    <p><code class="html example">&lt;foo bar=""></code></p>

    <p>... or like:</p>

    <p><code class="html example">&lt;foo bar=''></code></p>
  </d:desc>
</d:item>

<d:item name="invalid character reference"
    modules="HTML::Parser">
  <d:message xml:lang="en">Character reference to
  <code><var>{text}</var></code> is not allowed.</d:message>
</d:item>

<d:item name="nestc"
    modules="HTML::Parser">
  <d:message xml:lang="en">Polytheistic slash (<code>/></code>) cannot be
  used for this element.</d:message>
  <d:desc xml:lang="en">
    <p>Polytheistic slash (<code>/></code>) must not be used
    for the element.  The document is non-conforming.</p>

    <p>The polytheistic slash can only be
    used for <code>base</code>, <code>link</code>, <code>meta</code>,
    <code>hr</code>, <code>br</code>, <code>img</code>, 
    <code>embed</code>, <code>param</code>, <code>area</code>,
    <code>col</code>, and <code>input</code> elements.</p>

    <dl class="switch">
    <dt><code>&lt;script/></code></dt>
        <dd><p>The polytheistic slash cannot be used for <code>script</code>
        element.  Even for an empty <code>script</code> element,
        there must be an explicit end tag
        <code class="html example">&lt;/script></code>.</p>

        <p><strong>NOTE</strong>: Though some user agents interpret
        polytheistic slash for <code>script</code> element as the 
        closing of the element, such usage is not allowed under
        the current standard.</p></dd>
    <dt><code>&lt;basefont/></code>, <code>&lt;bgsound/></code>,
    <code>&lt;frame/></code>, <code>&lt;keygen/></code>,
    <code>&lt;spacer/></code>, <code>&lt;wbr/></code></dt>
        <dd>These elements are themselves non-conforming.</dd>
    <!-- isindex, image -->
    <dt><code>&lt;command/></code>, <code>&lt;event-source/></code>,
    <code>&lt;nest/></code>, or <code>&lt;source/></code></dt>
        <dd>Future revision of HTML5 parsing algorithm is expected
        to allow polytheistic slash for these elements.</dd>
    <dt><code>&lt;a/></code>, <code>&lt;p/></code></dt>
        <dd>These elements are not always empty and therefore
        polytheistic slash is not allowed.  Use explicit end tag
        to represent empty element as:
          <pre class="example html"><code>&lt;p>&lt;/p></code></pre>
        </dd>
    </dl>

    <p>Note that, unlike in XML, the polytheistic slash has
    no effect in HTML.</p>
  </d:desc>
</d:item>

<d:item name="no DOCTYPE name"
    modules="HTML::Parser">
  <d:message xml:lang="en">After the string <code>&lt;!DOCTYPE </code>, the
  document type name must be specified.</d:message>
</d:item>

<d:item name="no PUBLIC literal"
    modules="HTML::Parser">
  <d:message xml:lang="en">After the keyword <code>PUBLIC</code>, no
  oublic identifier is specified.</d:message>
</d:item>

<d:item name="no refc"
    modules="HTML::Parser">
  <d:message xml:lang="en">Character reference must be closed by a
  <code>;</code> character.</d:message>
</d:item>

<d:item name="no space before DOCTYPE name"
    modules="HTML::Parser">
  <d:message xml:lang="en">After the string <code>&lt;!DOCTYPE</code>, there
  must be at least a white space character before the document type
  name.</d:message>
</d:item>

<d:item name="no space between attributes"
    modules="HTML::Parser">
  <d:message xml:lang="en">Attributes must be separeted by at least a
  white space character.</d:message>
</d:item>

<d:item name="no SYSTEM literal"
    modules="HTML::Parser">
  <d:message xml:lang="en">After the keyword <code>SYSTEM</code>, no
  system identifier is specified.</d:message>
</d:item>

<d:item name="pio"
    modules="HTML::Parser">
  <d:message xml:lang="en">Processing instruction 
  (<code>&lt;?<var>...</var>></code>) is not allowed in HTML
  document.</d:message>
  <d:desc xml:lang="en">
    <p>Processing instructions (<code>&lt;?<var>...</var>?></code>),
    including XML declaration (<code>&lt;?xml <var>...</var>?></code>)
    and XML style sheet <abbr title="processing instruction">PI</abbr>
    (<code>&lt;?xml-stylesheet <var>...</var>?></code>), are not allowed 
    in the HTML syntax.  The document is non-conforming.</p>

    <dl class="switch">
    <dt><code>&lt;?xbl?></code> (<abbr>XBL</abbr> Association)</dt>
      <dd>An <abbr>XBL</abbr> binding cannot be associated by 
      <abbr title="processing instruction">PI</abbr> in <abbr>HTML</abbr>
      document.  Use <code>binding</code> property in <abbr>CSS</abbr>
      style sheet as:
        <pre class="html example"><code>&lt;style>
p {
  binding: url(binding.xbl);
}
&lt;/style></code></pre>
      </dd>
    <dt><code>&lt;?xml?&gt;</code> (XML declaration)</dt>
        <dd>XML declaration is unnecessary for HTML documents.</dd>
    <dt><code>&lt;?xml-stylesheet?></code> (XML style sheet
    <abbr title="processing instruction">PI</abbr>)</dt>
        <dd>Use HTML <code>link</code> element with <code>rel</code>
        attribute set to <code>stylesheet</code> (or,
        <code>alternate stylesheet</code> for an alternate style 
        sheet).
          <pre class="example html"><code>&lt;link rel=stylesheet href="path/to/stylesheet.css"></code></pre>
        </dd>
    <dt><code>&lt;?php?&gt;</code> or 
    <code>&lt;? <var>... <abbr>PHP</abbr> code ...</var> ?&gt;</code> 
    (<abbr>PHP</abbr> code)</dt>
        <dd>The conformance checker does <em>not</em> support
        checking for PHP source documents.</dd>
    <dt>Other processing instructions</dt>
        <dd>Processing instructions cannot be inserted in an HTML
        document.  Use XML document or insert 
        <code>ProcessingInstruction</code> node by scripting.</dd>
    </dl>

    <p>Web browsers will parse processing instructions as bogus
    comments.  Some legacy Web browsers, such as IE:mac and
    some mobile Web browsers, will display processing instructions
    as string.</p>
  </d:desc>
</d:item>

<d:item name="string after DOCTYPE name"
    modules="HTML::Parser">
  <d:message xml:lang="en">There is a bogus string after the document type
  name.</d:message>
</d:item>

<d:item name="string after PUBLIC"
    modules="HTML::Parser">
  <d:message xml:lang="en">There is a bogus string after the keyword
  <code>PUBLIC</code>.</d:message>
</d:item>

<d:item name="string after PUBLIC literal"
    modules="HTML::Parser">
  <d:message xml:lang="en">There is a bogus string after the public
  identifier.</d:message>
</d:item>

<d:item name="string after SYSTEM"
    modules="HTML::Parser">
  <d:message xml:lang="en">There is a bogus string after the keyword
  <code>SYSTEM</code>.</d:message>
</d:item>

<d:item name="string after SYSTEM literal"
    modules="HTML::Parser">
  <d:message xml:lang="en">There is a bogus string after the system
  identifier.</d:message>
</d:item>

<d:item name="unclosed attribute value"
    modules="HTML::Parser">
  <d:message xml:lang="en">Attribute value is not closed by a quotation
  mark.</d:message>
</d:item>

<d:item name="unclosed comment"
    modules="HTML::Parser">
  <d:message xml:lang="en">Comment is not closed by a string
  <code>--></code>.</d:message>
</d:item>

<d:item name="unclosed DOCTYPE"
    modules="HTML::Parser">
  <d:message xml:lang="en">The <code>DOCTYPE</code> is not closed by a
  <code>></code> character.</d:message>
</d:item>

<d:item name="unclosed PUBLIC literal"
    modules="HTML::Parser">
  <d:message xml:lang="en">The public identifier literal is not closed by a
  quotation mark.</d:message>
</d:item>

<d:item name="unclosed SYSTEM literal"
    modules="HTML::Parser">
  <d:message xml:lang="en">The system identifier literal is not closed by a
  quotation mark.</d:message>
</d:item>

<d:item name="unclosed tag"
    modules="HTML::Parser">
  <d:message xml:lang="en">Tag is not closed by a <code>></code>
  character.</d:message>
</d:item>

</section>

<section id="html5-parse-errors">
<h2>HTML5 Parse Errors in Tree Construction Stage</h2>

<d:item name="after after frameset"
    modules="HTML::Parser">
  <d:message xml:lang="en">There is a start tag
  <code>&lt;<var>{text}</var>></code> is after the <code>html</code> element
  is closed.</d:message>
  <d:message xml:lang="ja"><code>html</code> 要素が閉じられた後に開始タグ
  <code>&lt;<var>{text}</var>></code> があります。</d:message>
</d:item>

<d:item name="after after frameset:/"
    modules="HTML::Parser">
  <d:message xml:lang="en">There is an end tag
  <code>&lt;/<var>{text}</var>></code> is after the <code>html</code> element
  is closed.</d:message>
  <d:message xml:lang="ja"><code>html</code> 要素が閉じられた後に終了タグ
  <code>&lt;/<var>{text}</var>></code> があります。</d:message>
</d:item>

<d:item name="after body"
    modules="HTML::Parser">
  <d:message xml:lang="en">Start tag <code>&lt;<var>{text}</var>></code> is
  not allowed after the <code>body</code> is closed.</d:message>
</d:item>

<d:item name="after body:/"
    modules="HTML::Parser">
  <d:message xml:lang="en">End tag <code>&lt;/<var>{text}</var>></code> is
  not allowed after the <code>body</code> is closed.</d:message>
</d:item>

<d:item name="after body:#text"
    modules="HTML::Parser">
  <d:message xml:lang="en">Non‐white‐space characters are not allowed
  after the <code>body</code> is closed.</d:message>
</d:item>

<d:item name="after frameset"
    modules="HTML::Parser">
  <d:message xml:lang="en">Start tag <code>&lt;<var>{text}</var>></code> is
  not allowed after the <code>frameset</code> is closed.</d:message>
</d:item>

<d:item name="after frameset:/"
    modules="HTML::Parser">
  <d:message xml:lang="en">End tag <code>&lt;/<var>{text}</var>></code> is
  not allowed after the <code>frameset</code> is closed.</d:message>
</d:item>

<d:item name="after frameset:#text"
    modules="HTML::Parser">
  <d:message xml:lang="en">Non‐white‐space characters are not allowed
  after the <code>frame</code> is closed.</d:message>
</d:item>

<d:item name="after head"
    modules="HTML::Parser">
  <d:message xml:lang="en">The <code><var>{text}</var></code> element cannot be
  inserted between <code>head</code> and <code>body</code>
  elements.</d:message>
  <d:desc xml:lang="en">
    <p>A start tag appears after the <code>head</code> element is closed
    but before the <code>body</code> element is opened.
    The document is non-conforming.</p>
  </d:desc>
</d:item>

<d:item name="after html"
    modules="HTML::Parser">
  <d:message xml:lang="en">Start tag <code>&lt;<var>{text}</var>></code> is
  not allowed after the <code>html</code> is closed.</d:message>
  <d:desc xml:lang="en">
    <p>The start tag of an element appears after the
    <code>body</code> element has been closed.  The document is
    non-conforming.</p>

    <p>Any content of the document other than <code>head</code>
    contents and comments must be put into the <code>body</code>
    element.</p>
  </d:desc>
</d:item>

<d:item name="after html:/"
    modules="HTML::Parser">
  <d:message xml:lang="en">End tag <code>&lt;/<var>{text}</var>></code> is
  not allowed after the <code>html</code> is closed.</d:message>
  <d:desc xml:lang="en">
    <p>The end tag of an element appears after the
    <code>body</code> element has been closed.  The document is
    non-conforming.</p>

    <p>Any content of the document other than <code>head</code>
    contents and comments must be put into the <code>body</code>
    element.</p>
  </d:desc>
</d:item>

<d:item name="after html:#text"
    modules="HTML::Parser">
  <d:message xml:lang="en">Non‐white‐space characters are not allowed
  after the <code>html</code> is closed.</d:message>
</d:item>

<d:item name="image"
    modules="HTML::Parser">
  <d:message xml:lang="en">The <code>image</code> element is
  obsolete.</d:message>
</d:item>

<d:item name="in a:a"
    modules="HTML::Parser">
  <d:message xml:lang="en">Anchor cannot be nested.</d:message>
  <d:desc xml:lang="en">
    <p>HTML <code>a</code> elements cannot be nested.
    The document is non-conforming.</p>

    <p>In the HTML syntax, a start tag of the <code>a</code>
    implies the end tag of any opening <code>a</code> element.</p>
  </d:desc>
</d:item>

<d:item name="in body"
    modules="HTML::Parser">
  <d:message xml:lang="en">Start tag <code>&lt;<var>{text}</var>&gt;</code>
  is not allowed in the <code>body</code> element.</d:message>
  <d:desc xml:lang="en">
    <p>The start or end tag of an element, which 
    cannot be a descendant of <code>body</code> element, appears
    in the input stream while the <code>body</code> element has been opened.
    The document is non-conforming.</p>
  </d:desc>
</d:item>

<d:item name="in body:#eof"
    modules="HTML::Parser">
  <d:message xml:lang="en">Some element is not closed before the end of
  file.</d:message>
</d:item>

<d:item name="in button:button"
    modules="HTML::Parser">
  <d:message xml:lang="en">The <code>button</code> element cannot be
  nested.</d:message>
</d:item>

<d:item name="in CDATA:#eof"
    modules="HTML::Parser">
  <d:message xml:lang="en">Element is not closed before the end of
  file.</d:message>
</d:item>

<d:item name="in form:form"
    modules="HTML::Parser">
  <d:message xml:lang="en">Start tag <code>&lt;form></code> is
  not allowed in a <code>form</code> element.</d:message>
</d:item>

<d:item name="in frameset"
    modules="HTML::Parser">
  <d:message xml:lang="en">Start tag <code>&lt;<var>{text}</var>></code> is
  not allowed in a <code>framset</code> element.</d:message>
</d:item>

<d:item name="in frameset:/"
    modules="HTML::Parser">
  <d:message xml:lang="en">End tag <code>&lt;/<var>{text}</var>></code> is
  not allowed in a <code>frameset</code> element.</d:message>
</d:item>

<d:item name="in frameset:#text"
    modules="HTML::Parser">
  <d:message xml:lang="en">Non‐white‐space characters are not allowed
  in a <code>frameset</code> element.</d:message>
</d:item>

<d:item name="in head:head"
    modules="HTML::Parser">
  <d:message xml:lang="en">Start tag <code>&lt;head&gt;</code>
  is not allowed in the <code>head</code> element.</d:message>
  <d:desc xml:lang="en">
    <p>There is a start tag <code>&lt;head></code> in the
    <code>&lt;head></code> element.  The document is non-conforming.</p>

    <p>In an HTML document there must not be more than
    one <code>head</code> element, therefore no more than one
    start tag <code>&lt;head></code> can appear in the input stream.</p>
  </d:desc>
</d:item>

<d:item name="in html:#DOCTYPE"
    modules="HTML::Parser">
  <d:message xml:lang="en">A <code>DOCTYPE</code> appears after any
  element or data character has been seen.</d:message>
  <!-- <!DOCTYPE HTML><!DOCTYPE HTML> -->
  <!-- <html><!DOCTYPE HTML> -->
  <d:desc xml:lang="en">
    <p>A <code>DOCTYPE</code> appears after any element or data character
    has been seen.  The document is non-conforming.</p>
    
    <p>The <code>DOCTYPE</code> must be placed before any
    tag, reference, or data character.  Only white space characters
    and comments can be inserted before the <code>DOCTYPE</code>.</p>
  </d:desc>
</d:item>

<d:item name="in nobr:nobr"
    modules="HTML::Parser">
  <d:message xml:lang="en">The <code>nobr</code> element cannot be
  nested.</d:message>
</d:item>

<d:item name="in noscript"
    modules="HTML::Parser">
  <d:message xml:lang="en">The <code><var>{text}</var></code> element is not
  allowed in a <code>noscript</code> element in the
  <code>head</code> element.</d:message>
</d:item>

<d:item name="in noscript:/"
    modules="HTML::Parser">
  <d:message xml:lang="en">An end tag <code>&lt;/<var>{text}</var>></code>
  appers before the <code>noscript</code> element is closed.</d:message>
</d:item>

<d:item name="in noscript:#eof"
    modules="HTML::Parser">
  <d:message xml:lang="en">A <code>noscript</code> element is not closed
  before the end of file.</d:message>
</d:item>

<d:item name="in noscript:#text"
    modules="HTML::Parser">
  <d:message xml:lang="en">Non‐white‐space characters are not allowed
  in a <code>noscript</code> element in the <code>head</code>
  element.</d:message>
</d:item>

<d:item name="in PCDATA:#eof"
    modules="HTML::Parser">
  <d:message xml:lang="en">Element is not closed before the end of
  file.</d:message>
</d:item>

<d:item name="in select"
    modules="HTML::Parser">
  <d:message xml:lang="en">Start tag <code>&lt;<var>{text}</var>&gt;</code>
  is not allowed in a <code>select</code> element.</d:message>
</d:item>

<d:item name="in select:/"
    modules="HTML::Parser">
  <d:message xml:lang="en">End tag <code>&lt;/<var>{text}</var>&gt;</code>
  is not allowed in a <code>select</code> element.</d:message>
</d:item>

<d:item name="in table"
    modules="HTML::Parser">
  <d:message xml:lang="en">Start tag <code>&lt;<var>{text}</var>&gt;</code>
  is not allowed in a <code>table</code> element.</d:message>
  <d:desc xml:lang="en">
    <p>The start or end tag of an element, which
    cannot be a child of <code>table</code> element, appears
    in the input stream while the <code>table</code> element has been opened
    but no other element has been opened.  The document is non-conforming.</p>

    <p>In <code>table</code>, only table related elements
    are allowed; any other element must be contained in
    <code>td</code> or <code>th</code> element to form 
    a part of the table, or <code>caption</code> element to create
    a table caption.</p>
  </d:desc>
</d:item>

<d:item name="in table:/"
    modules="HTML::Parser">
  <d:message xml:lang="en">End tag <code>&lt;/<var>{text}</var>&gt;</code>
  is not allowed in a <code>table</code> element.</d:message>
</d:item>

<d:item name="in table:#text"
    modules="HTML::Parser">
  <d:message xml:lang="en">Non‐white‐space character is not allowed within 
  the <code>table</code> element, outside of the caption and cells.</d:message>
  <d:desc xml:lang="en">
    <p>A non‐white‐space character appears in <code>table</code>.
    The document is non-conforming.</p>

    <p>In <code>table</code>, only table related elements
    are allowed; any other element and data character must be contained in
    <code>td</code> or <code>th</code> element to form 
    a part of the table, or <code>caption</code> element to create
    a table caption.</p>
  </d:desc>
</d:item>

<d:item name="isindex"
    modules="HTML::Parser">
  <d:message xml:lang="en">The <code>isindex</code> element is
  obsolete.</d:message>
</d:item>

<d:item name="missing start tag:tr"