test/html-webhacc/error-description.en.html.u8

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<title xml:lang="en">Description of Errors — WebHACC (β)</title></head>
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<header>
<h1><a href="../cc-about"><abbr title="Web Hypertext Application Conformance Checker (β)"><img alt="WebHACC" src="../icons/title"></abbr></a></h1>
<h2>Description of Errors</h2>
</header>


<div class="section" id="WebHACC:Heading"><h3>
    
  </h3>
    <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>
  </div>

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

<div class="section" id="fallback-char-error"><h3>Octet sequence <code><var>{octets}</var></code>
  is not an allowed representation of the character
  <code><var>{char}</var></code> — character reference
  <code><var>{char:hexref}</var></code> should be used instead.</h3></div>

<div class="section" id="fallback-unassigned-error"><h3>No character is assigned to octet sequence
  <code><var>{octets}</var></code>.</h3></div>

<div class="section" id="illegal-octets-error"><h3>Octet sequence <code><var>{octets}</var></code>
  is illegal.</h3></div>

<div class="section" id="invalid-state-error"><h3>The input stream is broken.</h3>
    <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>
  </div>

<div class="section" id="unassigned-code-point-error"><h3>No character is assigned to octet sequence
  <code><var>{octets}</var></code>.</h3></div>
</section>

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

<div class="section" id="charset:not-supported"><h3>Character encoding <code><var>{value}</var></code>
  is not supported and the explicit character encoding specification is
  ignored.  The result of the conformance checking might be
  <em>wrong</em>.</h3></div>

<div class="section" id="disallowed-character-encoding"><h3>Character encoding <code><var>{text}</var></code>
  is not allowed for <abbr>HTML</abbr> document.</h3>
    <p>The character encoding used for the document is not allowed
    for <abbr>HTML</abbr> document.  The document is non‐conforming.</p>
  </div>

<div class="section" id="bad-character-encoding"><h3>Character encoding <code><var>{text}</var></code>
  should not be used for <abbr>HTML</abbr> document.</h3>
    <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>
  </div>

<div class="section" id="non-utf-8-character-encoding"><h3>Use of UTF-8 is encouraged (this document
  is encoded in <code><var>{text}</var></code>).</h3>
    <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>
  </div>

<div class="section" id="character-encoding-unchecked"><h3>Conformance for character encoding requirements
  cannot be checked, since the input is not a byte stream.</h3>
    <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>
  </div>

<div class="section" id="no-character-encoding-declaration"><h3>There is no character encoding
  declaration.</h3>
    <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>"&gt;</code>
    is obsolete.  The new syntax is:</p>
    <pre class="html example">
<code>&lt;meta charset="<var>charset-name</var>"&gt;</code></pre>

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

<div class="section" id="non-ascii-superset"><h3>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>.</h3>
    <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>"&gt;</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>
  </div>

<div class="section" id="sniffing:chardet"><h3>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).</h3></div>

<div class="section" id="sniffing:default"><h3>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.</h3></div>

<div class="section" id="chardecode:fallback"><h3>Results might be <em>wrong</em>, since the
  conformance checker cannot find an appropriate decoder for the character
  encoding used for the document.</h3>
    <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... -->
  </div>

<div class="section" id="chardecode:no-error"><h3>Conformance error checking for the character
  encoding <code><var>{text}</var></code> is not supported.</h3></div>

<div class="section" id="charset-label:matching"><h3>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.</h3></div>

<div class="section" id="charset-label-detected"><h3>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.</h3>
    <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>"&gt;</code>)
    just after <code class="html example">&lt;head&gt;</code> start tag.</li>
    <li>Use <code>UTF-8</code>.</li>
    </ul>
  </div>
</section>

<section id="character-set-layer">
<h2>Coded Character Set Layer Errors</h2>

<div class="section" id="NULL"><h3>The <code class="charname">NULL</code> character
  is not allowed.</h3></div>

<div class="section" id="control-char"><h3>Code point <code><var>{text}</var></code> is
  not allowed.</h3></div>

<div class="section" id="nonchar"><h3>Noncharacter <code><var>{text}</var></code>
  is found in the input stream.</h3>
    <p>Noncharacter code points are used in the input stream.</p>

    <p>Noncharacter code points are reserved for internal processings.
    Their use for information interchanges are forbidden.</p>

    <p>In addition, they are not allowed in HTML document.</p>
    <!-- "permanently undefined Unicode characters" in HTML5. -->
  </div>

<div class="section" id="non-unicode"><h3>Character <code><var>{text}</var></code> is not
  a Unicode character.</h3></div>

<div class="section" id="unicode-deprecated"><h3>Use of character <code><var>{text}</var></code>
  is deprecated.</h3></div>

<div class="section" id="unicode-discouraged"><h3>Use of character <code><var>{text}</var></code>
  is discouraged.</h3></div>

<div class="section" id="unicode-not-preferred"><h3>Code point <code><var>{text}</var></code>
  is not the preferred representation of that character.</h3></div>

<div class="section" id="unicode-should"><h3>Character <code><var>{text}</var></code>
  should not be used in many cases.</h3></div>

</section>

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

<div class="section" id="bad-attribute-name"><h3>Attribute name cannot contain characters
  <code>"</code>, <code>'</code>, and <code>=</code>.</h3></div>

<div class="section" id="bad-attribute-value"><h3>Attribute value must be quoted by <code>"</code>
  or <code>'</code> if it contains a <code>"</code>, <code>'</code>, or
  <code>=</code> character.</h3>
    <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=&gt;</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>
  </div>

<div class="section" id="bare-ero"><h3>The <code>&amp;</code> character must
  be escaped as <code class="html example">&amp;amp;</code>.</h3>
    <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>
  </div>

<div class="section" id="bare-etago"><h3>A <code>&lt;/</code> string is not followed
  by a tag name.</h3>
    <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>
  </div>

<div class="section" id="bare-stago"><h3>A <code>&lt;</code> character is not followed
  by tag name or by a <code>!</code> character.</h3>
    <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>
  </div>

<div class="section" id="bare-nero"><h3>The decimal representation of the code position
  of a character must be specified after <code>&amp;#</code>.</h3>
    <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>
  </div>

<div class="section" id="bare-hcro"><h3>The hexadecimal representation of the code position
  of a character must be specified after <code>&amp;#x</code>.</h3>
   <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>
  </div>

<div class="section" id="bogus-comment"><h3>String <code>&lt;!</code> is not followed
  by <code>--</code>.</h3>
    <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">--&gt;</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>
  </div>

<div class="section" id="bogus-end-tag"><h3>String <code>&lt;/</code> is not followed
  by tag name.</h3>
    <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>
  </div>

<div class="section" id="dash-in-comment"><h3>There is a <code>--</code> sequence
  in a comment.</h3>
    <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>
  </div>

<div class="section" id="duplicate-attribute"><h3>There are two attributes with name
      <code><var>{text}</var></code>.</h3>
    <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>
  </div>

<div class="section" id="empty-start-tag"><h3>Empty start tag (<code>&lt;&gt;</code>) is not
  allowed.</h3></div>

<div class="section" id="empty-end-tag"><h3>Empty end tag (<code>&lt;/&gt;</code>) is not
  allowed.</h3></div>

<div class="section" id="end-tag-attribute"><h3>End tag cannot have attributes.</h3></div>

<div class="section" id="empty-unquoted-attribute-value"><h3>Attribute value is not specified.</h3>
    <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&gt;</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=""&gt;</code></p>

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

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

<div class="section" id="invalid-character-reference"><h3>Character reference to
  <code><var>{text}</var></code> is not allowed.</h3></div>

<div class="section" id="nestc"><h3>Polytheistic slash (<code>/&gt;</code>) cannot be
  used for this element.</h3>
    <p>Polytheistic slash (<code>/&gt;</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/&gt;</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&gt;</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/&gt;</code>, <code>&lt;bgsound/&gt;</code>,
    <code>&lt;frame/&gt;</code>, <code>&lt;keygen/&gt;</code>,
    <code>&lt;spacer/&gt;</code>, <code>&lt;wbr/&gt;</code></dt>
        <dd>These elements are themselves non-conforming.</dd>
    <!-- isindex, image -->
    <dt><code>&lt;command/&gt;</code>, <code>&lt;event-source/&gt;</code>,
    <code>&lt;nest/&gt;</code>, or <code>&lt;source/&gt;</code></dt>
        <dd>Future revision of HTML5 parsing algorithm is expected
        to allow polytheistic slash for these elements.</dd>
    <dt><code>&lt;a/&gt;</code>, <code>&lt;p/&gt;</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&gt;&lt;/p&gt;</code></pre>
        </dd>
    </dl>

    <p>Note that, unlike in XML, the polytheistic slash has
    no effect in HTML.</p>
  </div>

<div class="section" id="no-DOCTYPE-name"><h3>After the string <code>&lt;!DOCTYPE </code>, the
  document type name must be specified.</h3></div>

<div class="section" id="no-PUBLIC-literal"><h3>After the keyword <code>PUBLIC</code>, no
  oublic identifier is specified.</h3></div>

<div class="section" id="no-refc"><h3>Character reference must be closed by a
  <code>;</code> character.</h3></div>

<div class="section" id="no-space-before-DOCTYPE-name"><h3>After the string <code>&lt;!DOCTYPE</code>, there
  must be at least a white space character before the document type
  name.</h3></div>

<div class="section" id="no-space-between-attributes"><h3>Attributes must be separeted by at least a
  white space character.</h3></div>

<div class="section" id="no-SYSTEM-literal"><h3>After the keyword <code>SYSTEM</code>, no
  system identifier is specified.</h3></div>

<div class="section" id="pio"><h3>Processing instruction 
  (<code>&lt;?<var>...</var>&gt;</code>) is not allowed in HTML
  document.</h3>
    <p>Processing instructions (<code>&lt;?<var>...</var>?&gt;</code>),
    including XML declaration (<code>&lt;?xml <var>...</var>?&gt;</code>)
    and XML style sheet <abbr title="processing instruction">PI</abbr>
    (<code>&lt;?xml-stylesheet <var>...</var>?&gt;</code>), are not allowed 
    in the HTML syntax.  The document is non-conforming.</p>

    <dl class="switch">
    <dt><code>&lt;?xbl?&gt;</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&gt;
p {
  binding: url(binding.xbl);
}
&lt;/style&gt;</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?&gt;</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"&gt;</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>
  </div>

<div class="section" id="string-after-DOCTYPE-name"><h3>There is a bogus string after the document type
  name.</h3></div>

<div class="section" id="string-after-PUBLIC"><h3>There is a bogus string after the keyword
  <code>PUBLIC</code>.</h3></div>

<div class="section" id="string-after-PUBLIC-literal"><h3>There is a bogus string after the public
  identifier.</h3></div>

<div class="section" id="string-after-SYSTEM"><h3>There is a bogus string after the keyword
  <code>SYSTEM</code>.</h3></div>

<div class="section" id="string-after-SYSTEM-literal"><h3>There is a bogus string after the system
  identifier.</h3></div>

<div class="section" id="unclosed-attribute-value"><h3>Attribute value is not closed by a quotation
  mark.</h3></div>

<div class="section" id="unclosed-comment"><h3>Comment is not closed by a string
  <code>--&gt;</code>.</h3></div>

<div class="section" id="unclosed-DOCTYPE"><h3>The <code>DOCTYPE</code> is not closed by a
  <code>&gt;</code> character.</h3></div>

<div class="section" id="unclosed-PUBLIC-literal"><h3>The public identifier literal is not closed by a
  quotation mark.</h3></div>

<div class="section" id="unclosed-SYSTEM-literal"><h3>The system identifier literal is not closed by a
  quotation mark.</h3></div>

<div class="section" id="unclosed-tag"><h3>Tag is not closed by a <code>&gt;</code>
  character.</h3></div>

</section>

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

<div class="section" id="after-after-frameset"><h3>There is a start tag
  <code>&lt;<var>{text}</var>&gt;</code> is after the <code>html</code> element
  is closed.</h3></div>

<div class="section" id="after-after-frameset:/"><h3>There is an end tag
  <code>&lt;/<var>{text}</var>&gt;</code> is after the <code>html</code> element
  is closed.</h3></div>

<div class="section" id="after-body"><h3>Start tag <code>&lt;<var>{text}</var>&gt;</code> is
  not allowed after the <code>body</code> is closed.</h3></div>

<div class="section" id="after-body:/"><h3>End tag <code>&lt;/<var>{text}</var>&gt;</code> is
  not allowed after the <code>body</code> is closed.</h3></div>

<div class="section" id="after-body:#text"><h3>Non‐white‐space characters are not allowed
  after the <code>body</code> is closed.</h3></div>

<div class="section" id="after-frameset"><h3>Start tag <code>&lt;<var>{text}</var>&gt;</code> is
  not allowed after the <code>frameset</code> is closed.</h3></div>

<div class="section" id="after-frameset:/"><h3>End tag <code>&lt;/<var>{text}</var>&gt;</code> is
  not allowed after the <code>frameset</code> is closed.</h3></div>

<div class="section" id="after-frameset:#text"><h3>Non‐white‐space characters are not allowed
  after the <code>frame</code> is closed.</h3></div>

<div class="section" id="after-head"><h3>The <code><var>{text}</var></code> element cannot be
  inserted between <code>head</code> and <code>body</code>
  elements.</h3>
    <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>
  </div>

<div class="section" id="after-html"><h3>Start tag <code>&lt;<var>{text}</var>&gt;</code> is
  not allowed after the <code>html</code> is closed.</h3>
    <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>
  </div>

<div class="section" id="after-html:/"><h3>End tag <code>&lt;/<var>{text}</var>&gt;</code> is
  not allowed after the <code>html</code> is closed.</h3>
    <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>
  </div>

<div class="section" id="after-html:#text"><h3>Non‐white‐space characters are not allowed
  after the <code>html</code> is closed.</h3></div>

<div class="section" id="image"><h3>The <code>image</code> element is
  obsolete.</h3></div>

<div class="section" id="in-a:a"><h3>Anchor cannot be nested.</h3>
    <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>
  </div>

<div class="section" id="in-body"><h3>Start tag <code>&lt;<var>{text}</var>&gt;</code>
  is not allowed in the <code>body</code> element.</h3>
    <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>
  </div>

<div class="section" id="in-body:#eof"><h3>Some element is not closed before the end of
  file.</h3></div>

<div class="section" id="in-button:button"><h3>The <code>button</code> element cannot be
  nested.</h3></div>

<div class="section" id="in-CDATA:#eof"><h3>Element is not closed before the end of
  file.</h3></div>

<div class="section" id="in-form:form"><h3>Start tag <code>&lt;form&gt;</code> is
  not allowed in a <code>form</code> element.</h3></div>

<div class="section" id="in-frameset"><h3>Start tag <code>&lt;<var>{text}</var>&gt;</code> is
  not allowed in a <code>framset</code> element.</h3></div>

<div class="section" id="in-frameset:/"><h3>End tag <code>&lt;/<var>{text}</var>&gt;</code> is
  not allowed in a <code>frameset</code> element.</h3></div>

<div class="section" id="in-frameset:#text"><h3>Non‐white‐space characters are not allowed
  in a <code>frameset</code> element.</h3></div>

<div class="section" id="in-head:head"><h3>Start tag <code>&lt;head&gt;</code>
  is not allowed in the <code>head</code> element.</h3>
    <p>There is a start tag <code>&lt;head&gt;</code> in the
    <code>&lt;head&gt;</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&gt;</code> can appear in the input stream.</p>
  </div>

<div class="section" id="in-html:#DOCTYPE"><h3>A <code>DOCTYPE</code> appears after any
  element or data character has been seen.</h3>
    <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>
  </div>

<div class="section" id="in-nobr:nobr"><h3>The <code>nobr</code> element cannot be
  nested.</h3></div>

<div class="section" id="in-noscript"><h3>The <code><var>{text}</var></code> element is not
  allowed in a <code>noscript</code> element in the
  <code>head</code> element.</h3></div>

<div class="section" id="in-noscript:/"><h3>An end tag <code>&lt;/<var>{text}</var>&gt;</code>
  appers before the <code>noscript</code> element is closed.</h3></div>

<div class="section" id="in-noscript:#eof"><h3>A <code>noscript</code> element is not closed
  before the end of file.</h3></div>

<div class="section" id="in-noscript:#text"><h3>Non‐white‐space characters are not allowed
  in a <code>noscript</code> element in the <code>head</code>
  element.</h3></div>

<div class="section" id="in-PCDATA:#eof"><h3>Element is not closed before the end of
  file.</h3></div>

<div class="section" id="in-select"><h3>Start tag <code>&lt;<var>{text}</var>&gt;</code>
  is not allowed in a <code>select</code> element.</h3></div>

<div class="section" id="in-select:/"><h3>End tag <code>&lt;/<var>{text}</var>&gt;</code>
  is not allowed in a <code>select</code> element.</h3></div>

<div class="section" id="in-table"><h3>Start tag <code>&lt;<var>{text}</var>&gt;</code>
  is not allowed in a <code>table</code> element.</h3>
    <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>
  </div>

<div class="section" id="in-table:/"><h3>End tag <code>&lt;/<var>{text}</var>&gt;</code>
  is not allowed in a <code>table</code> element.</h3></div>

<div class="section" id="in-table:#text"><h3>Non‐white‐space character is not allowed within 
  the <code>table</code> element, outside of the caption and cells.</h3>
    <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>
  </div>

<div class="section" id="isindex"><h3>The <code>isindex</code> element is
  obsolete.</h3></div>

<div class="section" id="missing-start-tag:tr"><h3>Start tag of <code>tr</code>
  element is missing.</h3>
    <p>Start tag of a <code>tr</code> element, which is <em>not</em>
    optional, is missing.  The document is non-conforming.</p>

    <p>In a table section, a <code>&lt;tr&gt;</code> start tag
    must occur before any <code>&lt;td&gt;</code> or
    <code>&lt;th&gt;</code> start tag.  Though the HTML5 parser
    implies the <code>&lt;tr&gt;</code> start tag before
    these start tags, it must be explicitly specified.</p>
  </div>

<div class="section" id="no-DOCTYPE"><h3>This document does not start with a
  <code>DOCTYPE</code>.</h3>
    <p>The document does not start with a <code>DOCTYPE</code>.
    The document is non-conforming.</p>

    <p>An HTML document must start by a <code>DOCTYPE</code>:
      <pre class="html example">
<code>&lt;!DOCTYPE HTML&gt;</code></pre>
    </p>

    <p>Only white space characters and comments are allowed
    before the <code>DOCTYPE</code>.  XML declaration is <em>not</em>
    allowed in HTML document.</p>
  </div>

<div class="section" id="not-closed"><h3>Element <code><var>{text}</var></code> is not
  closed.</h3>
    <p>End tag of an element is not found before, for example,
    an end tag of another element appears or
    the end of the document.  The document is non-conforming.</p>

    <p>Only <code>body</code>, <code>colgroup</code>, <code>dd</code>,
    <code>dt</code>, <code>head</code>, <code>html</code>, <code>li</code>,
    <code>ol</code>, <code>option</code>, <code>optgroup</code>, 
    <code>p</code>, <code>rb</code>, <code>rp</code>, <code>rt</code>,
    <code>tbody</code>, <code>td</code>, <code>tfoot</code>,
    <code>th</code>, <code>thead</code>, <code>tr</code>,
    <code>ul</code> end tag can be omitted in HTML documents.
    For any element except for void element, there must be an explicit
    end tag.</p>

    <dl class="switch">
    <dt>HTML <code>canvas</code> element</dt>
      <dd>Though the element is void in earlier versions of Safari,
      the <code>canvas</code> element is <em>no</em> longer
      defined as empty.  There must be an end tag
      <code class="html example">&lt;/canvas&gt;</code>.</dd>
    </dl>

    <p>Note that misnesting tags, such as 
    <code class="bad example">&lt;a&gt;&lt;b&gt;&lt;/a&gt;&lt;/b&gt;</code>, are not
    allowed and they also cause this error.</p>
  </div>

<div class="section" id="not-first-start-tag"><h3>This <code>&lt;html&gt;</code> tag is not
  the first start tag.</h3>
    <p>There is a start tag of the <code>html</code> element
    that it not the first start tag in the input stream.
    The document is non-conforming.</p>

    <p>In an HTML document, there cannot be more than one
    <code>html</code> element and therefore there cannot be
    more than one <code>&lt;html&gt;</code> tag.  In addition,
    nothing can be placed before the <code>&lt;html&gt;</code> tag
    except a <code>DOCTYPE</code>, white space characters, 
    and comments.</p>
  </div>

<div class="section" id="not-HTML5"><h3>This document is written in an old version of 
  HTML.</h3>
    <p>The document contains a <code>DOCTYPE</code> declaration
    that is different from HTML5 <code>DOCTYPE</code> (i.e. 
    <code class="example html">&lt;!DOCTYPE HTML&gt;</code>).
    The document is non‐conforming.</p>

    <p>The document might or might not be conformant to
    some version of HTML.  However, conformance to any HTML
    specification other than HTML5 provides for no practical
    convenience, since Web borwsers will parse any
    HTML document (roughly) as defined in HTML5.</p>
  </div>

<div class="section" id="start-tag-not-allowed"><h3>Start tag <code>&lt;<var>{text}</var>&gt;</code> is
  not allowed here.</h3></div>

<div class="section" id="unmatched-end-tag"><h3>Element <code><var>{text}</var></code> is not
  opened.</h3>
    <p>An end tag appears though no element with the same name
    has been opened.  The document is non-conforming.</p>

    <p>For any end tag in HTML document, there must be a
    corresponding start tag.</p>

    <dl class="switch">
    <dt>HTML <code>base</code>, <code>basefont</code>,
    <code>bgsound</code>, <code>br</code>, <code>col</code>,
    <code>embed</code>, <code>frame</code>, <code>hr</code>,
    <code>image</code>, <code>img</code>, <code>input</code>,
    <code>isindex</code>, <code>link</code>, <code>meta</code>,
    <code>param</code>, <code>spacer</code>, or <code>wbr</code> element</dt>
      <dd>End tag is not allowed for these elements, since
      those content must always be empty.  Remove end tag.</dd>
    <!-- keygen -->
    <!-- command, event-source, nest, source -->
    </dl>
  </div>

<div class="section" id="XSLT-compat"><h3>The <code>DOCTYPE</code> legacy string is
  used.</h3>
    <p>The <code>DOCTYPE</code> with the <code>DOCTYPE</code> legacy
    string, i.e.
    <code class="html bad example">&lt;!DOCTYPE HTML PUBLIC "XSLT-compat"&gt;</code>
    is used.</p>

    <p>The <code>DOCTYPE</code> legacy string should not be used for documents
    <em>not</em> generated from XSLT transformation process.  It is allowed
    only to enable to use XSLT style sheets with the HTML output mode, which
    does not support generation of the <code>DOCTYPE</code> with no
    <code>PUBLIC</code>
    identifier.  For other purposes, the <code>DOCTYPE</code> legacy
    string, i.e. <code class="html bad example">PUBLIC "XSLT-compat"</code>,
    is useless and should not be used.</p>
  </div>

</section>

<section id="element-content-model-errors">
<h2>Element Content Model Errors</h2>

<div class="section" id="basehref-after-URL-attribute"><h3>The <code>base</code> element with the 
  <code>href</code> attribute specified cannot be placed after
  any attribute with a URL.</h3></div>

<div class="section" id="basetarget-after-hyperlink"><h3>The <code>base</code> element with the
  <code>target</code> attribute specified cannot be placed after
  any element that defines a hyperlink.</h3></div>

<div class="section" id="character-not-allowed"><h3>Data character is not allowed in this
  context.</h3>
    <p>A data character appears where it is not allowed in this
    context.  The document is non-conforming.</p>

    <p>Possible causes:
      <ul>
      <li><p>A data character cannot be a child
      of certain sectioning elements such as <code>body</code>,
      <code>section</code>, and <code>blockquote</code>.</p>

      <p>Any inline-level content must be put
      in e.g. paragraph element such as <code>p</code>.</p></li>
      <li><p>Though some elements such as <code>div</code>,
      <code>li</code>, and <code>td</code> allow
      <em>either one</em> of block-level or inline-level content
      is allowed.  If there is a block-level content, 
      any inline-level content must be put
      in e.g. paragraph element such as <code>p</code>.</p></li>
      </ul>
    </p>
  </div>

<div class="section" id="character-not-allowed:empty"><h3>Non‐white‐space characters are not allowed in
  an empty element.</h3></div>

<div class="section" id="character-not-allowed:atom|PersonConstruct"><h3>Non‐white‐space characters are not allowed in
  Person construct.</h3></div>

<div class="section" id="character-not-allowed:atom|TextConstruct"><h3>Non‐white‐space characters are not allowed in
  Text construct.</h3></div>

<div class="section" id="child-element-missing"><h3>There must be an element
  <code><var>{text}</var></code> as a child of this element.</h3>
    <p>The content model of the element is so defined that it
    must contain a <code><var>$0</var></code> child element.
    The document is non-conforming.</p>

    <dl class="switch">
    <dt>HTML <code>head</code> element</dt>
      <dd>There must be a <code>title</code> child element.</dd>
    <dt>HTML <code>html</code> element</dt>
      <dd>There must be a <code>head</code> child element followed
      by a <code>body</code> element.</dd>
    <dt>HTML <code>tr</code> element</dt>
      <dd><a href="#child-element-missing:td%7Cth">There must be
      one or more <code>td</code> or <code>th</code> child element.</a></dd>
    </dl>
  </div>

<div class="section" id="child-element-missing:td|th"><h3>There must be a <code>td</code>
  or <code>th</code> element as a child of this element.</h3>
    <p>The <code>tr</code> element must contain at least one
    <code>td</code> or <code>th</code> child element.  The document
    is non-conforming.</p>
  </div>

<div class="section" id="child-element-missing:atom"><h3>There must be an element
  <code><var>{text}</var></code> in the Atom namespace as a child of this
  element.</h3></div>

<div class="section" id="child-element-missing:atom:link:alternate"><h3>There must be an Atom <code>link</code> element
  whose <code>rel</code> attribute is set to <code>alternate</code> as a
  child of this element.</h3></div>

<div class="section" id="child-element-missing:atom:link:self"><h3>There should be an Atom <code>link</code> element
  whose <code>rel</code> attribute is set to <code>self</code> as a
  child of this element.</h3></div>

<div class="section" id="element-missing:hn"><h3>There must be at least one 
  <code>h<var>n</var></code> element descendant.</h3></div>

<div class="section" id="element-not-allowed"><h3>This element is not allowed in this 
  context.</h3>
    <p>An element appears where it is not allowed.  The document
    is non-conforming.</p>

    <p>Possible causes:
      <dl class="switch">
      <dt>If the element with the error is an inline-level element,
      such as <code>a</code>, <code>progress</code>, or <code>img</code></dt>
          <dd><p>An inline-level element cannot be a child
          of certain sectioning elements such as <code>body</code>,
          <code>section</code>, and <code>blockquote</code>.</p>

          <p>Any inline-level content must be put
          in e.g. paragraph element such as <code>p</code>.</p></dd>
      <dt>If it is a block-level elements, such as <code>aside</code>,
      <code>div</code>, <code>h<var>n</var></code>,
      <code>p</code>, or <code>section</code></dt>
          <dd><dl class="switch">
              <dt>If the parent element is <code>div</code>,
              <code>li</code>, <code>td</code>, or <code>th</code></dt>
              <!-- @@ TODO: more... -->
                  <!-- @@ TODO: <p><ul><li><p> -->
                  <dd><p>The parent element allows <em>either</em>
                  block-level or inline-level content.  If there is a
                  block-level content, any inline-level content must be
                  put in e.g. paragraph element such as <code>p</code>.</p>
                  <p>For example, an HTML document fragment
                  <code class="html bad example">&lt;div&gt;&lt;p&gt;Hello!&lt;/p&gt; World!&lt;/div&gt;</code>
                  is non-conforming, since a word <q>World!</q> does not belong
                  to any paragraph.  (If not part of any paragraph, what is
                  it!?)  A conforming example would be:
                    <pre class="html example">
<code>&lt;div&gt;&lt;p&gt;Hello!&lt;/p&gt; &lt;p&gt;World!&lt;/p&gt;&lt;/div&gt;</code></pre>
                  </p></dd>
              <dt>If the parent element does <em>not</em> allow 
              block-level elements as content</dt>
                  <dd>The element is not allowed to be inserted here.
                  For example, a <code>div</code> element cannot be 
                  a child of an <code>h1</code> element.</dd>
          </dl></dd>
      <dt>If the element with the error is a <code>noscript</code> element</dt>
          <dd>The <code>noscript</code> element is allowed only in the context
          where a block-level or inline-level content is expected
          and in the <code>head</code> element.
          It cannot be used in e.g. <code>ul</code>, <code>table</code>,
          or <code>select</code>.</dd>
      <dt>If the element with the error is <code>blink</code>,
      <code>center</code>, or <code>marquee</code> element</dt>
          <dd>These elements are not part of the HTML standard.
          Use CSS for styling control.</dd>

      <dt><code>button</code>, <code>datalist</code>,
      <code>fieldset</code>, <code>form</code>,
      <code>input</code>, <code>label</code>,
      <code>optgroup</code>, <code>option</code>, <code>output</code>,
      <code>rb</code>, <code>rp</code>, <code>rt</code>, <code>ruby</code>,
      <code>textarea</code>, or <code>textarea</code> element</dt>
      <!-- rbc, rtc ? -->
          <dd>These elements are intentionally not supported by the conformance
          checker <em>yet</em>.</dd>
      </dl>
    </p>
  </div>

<div class="section" id="element-not-allowed:area"><h3>An <code>area</code> element cannot be used
  outside of a <code>map</code> element.</h3></div>

<div class="section" id="element-not-allowed:base"><h3>There is another <code>base</code>
  element.</h3></div>

<div class="section" id="element-not-allowed:datatemplate"><h3>In a <code>datatemplate</code> element, only
  <code>rule</code> elements are allowed.</h3></div>

<div class="section" id="element-not-allowed:details-legend"><h3>In a <code>details</code> or <code>fieldset</code>
  element, only at the beginning of the element a <code>legend</code> element
  may be used.</h3></div>

<div class="section" id="element-not-allowed:empty"><h3>Elements are not allowed in an empty
  element.</h3></div>

<div class="section" id="element-not-allowed:figure-legend"><h3>In a <code>figure</code> element, only at the
  beginning or only at the end of the element a <code>lengend</code> element
  may be used.</h3></div>

<div class="section" id="element-not-allowed:flow"><h3>This element is not allowed where flow
  content is expected.</h3></div>

<div class="section" id="element-not-allowed:flow-style"><h3>A <code>style</code> element without
  <code>scoped</code> attribute is not allowed in this context.</h3></div>

<div class="section" id="element-not-allowed:head-noscript"><h3>This element is not allowed in a
  <code>noscript</code> element in the <code>head</code> element.</h3></div>

<div class="section" id="element-not-allowed:head-style"><h3>A <code>style</code> element with
  <code>scoped</code> attribute is not allowed in the <code>head</code>
  element.</h3></div>

<div class="section" id="element-not-allowed:head-title"><h3>There is another <code>title</code>
  element.</h3></div>

<div class="section" id="element-not-allowed:minus"><h3>This element is not allowed in this
  context.</h3></div>

<div class="section" id="element-not-allowed:meta-charset"><h3>The character encoding declaration is not the
  first child element in the <code>head</code> element.</h3>
    <p>The character encoding declaration
    (<code class="html example">&lt;meta charset="<var>...</var>"&gt;</code> or
    <code class="html example">&lt;meta http-equiv=Content-Type content="text/html; charset=<var>...</var>"&gt;</code>
    must be the first child element in the <code>head</code> element.</p>

    <p>The character encoding declaration have to occur near the beginning
    of the document to ensure that Web browsers can be determine the
    character encoding of the document.</p>

    <p>The <code>title</code> element and other metadata elements must
    appear after any character encoding declaration is processed.</p>
  </div>

<div class="section" id="element-not-allowed:metadata"><h3>This element is not allowed where metadata
  content is expected.</h3></div>

<div class="section" id="element-not-allowed:phrasing"><h3>This element is not allowed where phrasing
  content is expected.</h3></div>

<div class="section" id="element-not-allowed:root"><h3>This element is not allowed as the root
  element of a document.</h3>
    <p>An element that is not allowed as the root element
    is used as the root element of the document.  The document is
    non-conforming, as far as the conformance checker can tell.</p>

    <dl class="switch">
    <dt><code>html</code> element in an XHTML document</dt>
        <dd><p>In <abbr>XHTML</abbr> document, the root <code>html</code>
        element must have an <code>xmlns</code> attribute as:
          <pre class="xml example">
<code>&lt;html xmlns="http://www.w3.org/1999/xhtml"&gt;</code></pre></p></dd>
    <dt><code>rss</code> element</dt>
        <dd><p>The document is written in some version of RSS.</p>
        <p>The conformance checker does not support any version
        of RSS.  Use Atom 1.0 for feed documents.</p></dd>
    <dt><code>feed</code> element</dt>
        <dd><p>The Atom <code>feed</code> element must be
        in the <code>http://www.w3.org/2005/Atom</code>
        namespace as:
          <pre class="xml example">
<code>&lt;feed xmlns="http://www.w3.org/2005/Atom"&gt;</code></pre>
        </p>
        <p>The conformance checker does not support Atom 0.3.
        Use Atom 1.0 for feed documents.</p></dd>
    </dl>
  </div>

<div class="section" id="element-not-allowed:root:xml"><h3>This element is not allowed as the root element
  of an XML document.</h3></div>

<div class="section" id="element-not-allowed:ruby-base"><h3>This element is not allowed in the <code>ruby</code>
  element.</h3></div>

<div class="section" id="element-not-allowed:text"><h3>This element is not allowed in this
  context.</h3></div>

<div class="section" id="element-not-allowed:atom|content"><h3>This element is not allowed in an Atom
  <code>content</code> element.</h3></div>

<div class="section" id="element-not-allowed:atom|PersonConstruct"><h3>This element is not allowed in Person
  construct.</h3></div>

<div class="section" id="element-not-allowed:atom|TextConstruct"><h3>This element is not allowed in Text
  construct.</h3></div>

<div class="section" id="element-not-defined"><h3>This element is not defined.</h3>
    <p>The element is not one of elements allowed
    in the latest version of relevant specifications.</p>

    <p>The element cannot be used.</p>

    <dl class="switch">
    <dt><code>event-source</code> element</dt>
        <dd>The element was renamed as <em><code>eventsource</code>
        element</em> (no hyphen).</dd>
    <dt><code>m</code> element</dt>
        <dd>The element was renamed as <em><code>mark</code>
        element</em>.</dd>
    </dl>
  </div>

<div class="section" id="multiple-labelable-fae"><h3>More than one labelable form-associated element
  is associated to a <code>label</code> element.</h3></div>

<div class="section" id="no-significant-content"><h3>No significant content is contained
  in this element.</h3></div>

<div class="section" id="no-significant-content-before"><h3>There is no significant content
  before this element.</h3></div>

<div class="section" id="no-significant-content-at-the-end"><h3>No significant content is contained
  at the end of this element.</h3></div>

<div class="section" id="ps-element-missing"><h3>There is no <code><var>{text}</var></code>
  element before this element.</h3>
    <p>There must be an element before another element, but there
    is not.  The document is non-conforming.</p>

    <p>For example, there must be a <code>dt</code> element
    before any <code>dd</code> element.</p>
  </div>

<div class="section" id="rp:syntax-error"><h3>The content of a <code>rp</code> element must
  be a parenthesis.</h3></div>

</section>

<section id="attribute-errors">
<h2>Attribute Errors</h2>

<div class="section" id="attribute-missing"><h3>Required attribute <code><var>{text}</var></code>
  is not specified.</h3>
    <p>A required attribute is not specified.  The document
    is non-conforming.</p>

    <p>Some attribute is defined as <i>required</i>.
    Without required attributes specified, user agents 
    cannot provide full functionality of the element to the user.</p>

    <dl class="switch">
    <dt>HTML <code>img</code> element</dt>
        <dd>The <code>src</code> attribute must be specified.
        Additionally, the <code>alt</code> attribute must be specified
        in many cases.</dd>
    <dt>HTML <code>link</code> element</dt>
        <dd>The <code>rel</code> attribute must be specified.
        Note that the <code>rev</code> attribute is obsolete.</dd>
    </dl>
  </div>

<div class="section" id="attribute-missing:data|type"><h3>For an <code>object</code> at least one of
  <code>data</code> and <code>type</code> attributes must be 
  specified.</h3></div>

<div class="section" id="attribute-missing:href|target"><h3>For a <code>base</code> element, at least one of
  <code>href</code> and <code>target</code> attributes must be
  specified.</h3></div>

<div class="section" id="attribute-missing:name|http-equiv"><h3>For a <code>meta</code> element with the
  <code>content</code> attribute specified, exactly one of
  <code>name</code> and <code>http-equiv</code> attributes must be
  specified.</h3></div>

<div class="section" id="attribute-missing:name|http-equiv|charset"><h3>For a <code>meta</code> element, exactly one of
  <code>name</code>, <code>http-equiv</code>, and <code>charset</code>
  attributes must be specified.</h3></div>

<div class="section" id="attribute-not-allowed"><h3>Attribute
  <code><var>{local-name}</var></code> is not allowed for
  <code><var>{element-local-name}</var></code> element.</h3>
    <p>An attribute is specified where it is not allowed.
    The document is non-conforming.</p>

    <dl>
    <dt>HTML <code>meta</code> element</dt>
        <dd>For HTML <code>meta</code> element, <em>only one</em> of
        <code>name</code>, <code>http-equiv</code>, or <code>charset</code>
        attribute is allowed.</dd>
    </dl>
  </div>

<div class="section" id="attribute-not-allowed:ismap"><h3>The <code>ismap</code> attribute may only be
  used for the image contained in an <code>a</code> element.</h3></div>

<div class="section" id="attribute-not-defined"><h3>This attribute is not defined.</h3>
    <p>The attribute is not one of attributes allowed for the element
    in the latest version of relevant specifications.</p>

    <p>The attribute cannot be used.</p>

    <dl class="switch">
    <dt><code>align</code> attribute (various HTML elements)</dt>
    <dt><code>border</code> attribute (various HTML elements)</dt>
      <dd>These attributes are no longer part of HTML.  You can use CSS
      properties to control the presentation of the element.</dd>
    <dt><code>autosubmit</code> attribute (<code>menu</code> element)</dt>
      <dd>The attribute was part of HTML5 draft but then dropped.
      Similar functionality can be implemented by scripts.</dd>
    <dt><code>language</code> attribute (<code>script</code> element)</dt>
      <dd>The attribute is no longer the standard way to specify the
      scripting language.  If you are using JavaScript, then no explicit
      specification of the scripting language is necessary, so you can
      write the element like:
        <p><code class="html example code">&lt;script&gt;<br><!--
        --> /* JavaScript code */<br><!--
        -->&lt;/script&gt;</code></p>
      If you are using different scripting language from JavaScript, or 
      you want to declare the scripting language explicitly, you should
      use the <code>type</code> attribute, as follows:
        <dl class="switch">
        <dt>JavaScript</dt>
          <dd>Use
          <code class="html example">&lt;script type="text/javascript"&gt;</code>.</dd>
        <dt>VBScript</dt>
          <dd>Use
          <code class="html example">&lt;script type="text/vbscript"&gt;</code>.</dd>
        </dl>
      </dd>
    </dl>
  </div>

<div class="section" id="_charset_-value"><h3>The <code>value</code> attribute cannot be 
  specified to an <code>input</code> element whose <code>type</code>
  is <code>hidden</code> and <code>name</code> is
  <code>_charset_</code>.</h3></div>

<div class="section" id="in-HTML:xml:lang"><h3>The <code>xml:lang</code> attribute in HTML
  document is ignored.</h3>
    <p>The <code>xml:lang</code> attribute does not have an effect in
    HTML document.</p>

    <p>The <code>xml:lang</code> attribute is only applicable to XML
    documents.  In HTML document, it is only allowed to ease migration
    from XML.</p>

    <p>To specify natural language information in HTML document,
    use <code>lang</code> attribute instead.</p>

    <p>XHTML 1.0 Appendix C was encouraged to specify both
    <code>lang</code> and <code>xml:lang</code> attributes with
    the same value.  Such a duplication has <em>no effect</em> in practice.
    Use only one of <code>lang</code> (in HTML) or <code>xml:lang</code> (in
    XML).</p>

    <!-- @@ ISSUE: xml:lang in non-HTML element in DOM5 HTML created
         from an HTML document? -->
  </div>

<div class="section" id="in-XML:charset"><h3>The <code>charset</code> attribute is not 
  allowed in XML document.</h3>
    <p>The <code>charset</code> attribute of a
    <code>meta</code> element is not allowed in XML document.
    The document is non-conforming.</p>

    <p>To specify the character encoding used for serialization,
    if necessary, use XML declaration instead:
      <pre class="xml example">
<code>&lt;?xml version="1.0" encoding="<var>encoding-name</var>"?&gt;</code></pre>
    </p>
  </div>

<div class="section" id="in-XML:noscript"><h3>A <code>noscript</code> element cannot be 
  used in XML document.</h3></div>

<div class="section" id="in-XML:xml:lang"><h3>The <code>xml:lang</code> attribute in no namespace
  is only allowed in HTML document.</h3></div>

<div class="section" id="in-XML:xmlns"><h3>The <code>xmlns</code> attribute 
  in the <code>null</code> namespace is not allowed in
  XHTML document.  The document is non-conforming.</h3>
    <p>The <code>xmlns</code> attribute in the <code>null</code>
    namespace is not allowed in XHTML document.</p>

    <p>This error should not occur in conformance-checking of
    static documents.</p>
  </div>

<div class="section" id="input-attr-not-applicable"><h3>This attribute is not applied to an 
  <code>input</code> element whose <code>type</code> is 
  <code><var>{text}</var></code>.</h3></div>

<div class="section" id="non-ol-li-value"><h3>The <code>value</code> attribute cannot be 
  specified to a <code>li</code> element whose parent element is
  not an <code>ol</code> element.</h3></div>

<div class="section" id="xml:lang-not-allowed"><h3>The <code>xml:lang</code> attribute is only allowed
  when the <code>lang</code> attribute is specified.</h3></div>

</section>

<section id="attribute-value-errors">
<h2>Attribute Value Errors</h2>

<div class="section" id="boolean:invalid"><h3>Attribute value <code><var>{@}</var></code>
  is not allowed.  It must be an empty string or a string
  <code><var>{local-name}</var></code>.</h3></div>

<div class="section" id="char:syntax-error"><h3>The attribute value must be exactly one
  character.</h3></div>

<div class="section" id="charref-in-charset"><h3>A character reference cannot be used to
  represent a character encoding name.</h3></div>

<div class="section" id="charset:not-ascii-compat"><h3>Characeter encoding <code><var>{value}</var></code>
  is not ASCII compatible.</h3></div>

<div class="section" id="charset:not-preferred"><h3>Character encoding name
  <code><var>{value}</var></code> is not the preferred name of that
  character encoding.</h3></div>

<div class="section" id="charset:not-registered"><h3>Character encoding name
  <code><var>{value}</var></code> is not a registered name.</h3>
    <p>The specified character encoding name is not registered to
    <abbr>IANA</abbr>.  Use of registered character encoding name
    is a good practice to facilitate interoperability.</p>

    <dl class="switch">
    <dt><code>EUC-TW</code></dt>
      <dd><code>EUC-TW</code> is not registered.  Unfortunately, there
      is no registered name for that character encoding.  Use
      Big5 encoding with character encoding name <code>Big5</code> 
      if it is enough to represent the document.</dd>
    <dt><code>ISO-2022-JP-1</code></dt>
      <dd><code>ISO-2022-JP-1</code> is not registered, nevertheless
      this character encoding name is documented in 
      <a href="urn:ietf:rfc:2237"><abbr>RFC</abbr> 2237</a>.  Use
      <code>ISO-2022-JP-2</code> instead, since that character encoding
      is a superset of ISO-2022-JP-1.</dd>
    <dt><code>ISO-2022-JP-3</code>, <code>ISO-2022-JP-3-plane1</code></dt>
      <dd>These names are not registered and obsoleted in favor of
      <code>ISO-2022-JP-2004</code> and
      <code>ISO-2022-JP-2004-plane1</code>.</dd>
    <dt><code>ISO-2022-JP-2003</code>,
    <code>ISO-2022-JP-2003-plane1</code></dt>
      <dd>These names are not registered and corrected to
      <code>ISO-2022-JP-2004</code> and
      <code>ISO-2022-JP-2004-plane1</code>.</dd>
    <dt><code>ISO-2022-JP-2004</code>,
    <code>ISO-2022-JP-2004-plane1</code></dt>
      <dd>These names are not registered.  Unfortunately, there is 
      no registered name for these character encodings.</dd>
    <dt><code>UTF-8N</code></dt>
      <dd><code>UTF-8N</code> is not registered.  Character encoding
      name <code>UTF-8</code> represents UTF-8 encoding with or
      without <abbr>BOM</abbr>.</dd>
    </dl>

    <p><strong>WARNING</strong>: This error might be raised for
    a registered character encoding name, since the character encoding
    name database of the conformance checker is not complete yet.</p>
  </div>

<div class="section" id="charset:private"><h3>Character encoding name
  <code><var>{value}</var></code> is a private name.</h3>
    <p>The specified character encoding name is a private name and
    not registered to <abbr>IANA</abbr>.  Use of registered character
    encoding name is a good practice to facilitate interoperability.</p>

    <dl class="switch">
    <dt><code>x-euc-jp</code></dt>
      <dd>Use <code>EUC-JP</code> for the Japanese <abbr>EUC</abbr>
      character encoding.</dd>
    <dt><code>x-sjis</code></dt>
      <dd>Use <code>Shift_JIS</code> for standard Shift encoding scheme of
      <abbr>JIS</abbr> coded character set, or <code>Windows-31J</code>
      for Microsoft standard character set as implemented by
      Microsoft Windows.</dd>
    </dl>
  </div>

<div class="section" id="charset:syntax-error"><h3>The specified value <code><var>{value}</var></code>
  is syntactically not a character encoding name.</h3>
    <p>The attribute value must be a character encoding name.  However,
    the specified value is not a character encoding name syntactically.
    The document is non‐conforming.</p>
    <p>Character encoding name is a string of <abbr>ASCII</abbr>
    printable characters, up to 40 characters.</p>
  </div>

<div class="section" id="color:syntax-error"><h3>The specified value is not a color
  name or hexadecimal color number.</h3></div>

<div class="section" id="coords:number-not-3"><h3>The <code>coords</code> attribute have to
  contain three (3) numbers (specified:
  <code><var>{text}</var></code>).</h3></div>

<div class="section" id="coords:number-not-4"><h3>The <code>coords</code> attribute have to
  contain four (4) numbers (specified:
  <code><var>{text}</var></code>).</h3></div>

<div class="section" id="coords:number-lt-6"><h3>The <code>coords</code> attribute have to
  contain more than or equal to six (6) numbers (specified:
  <code><var>{text}</var></code>).</h3></div>

<div class="section" id="coords:number-not-even"><h3>The <code>coords</code> attribute have to
  contain even number of numbers (specified:
  <code><var>{text}</var></code>).</h3></div>

<div class="section" id="coords:out-of-range"><h3>The specified value <code><var>{value}</var></code>
  is out of range.</h3></div>

<div class="section" id="coords:syntax-error"><h3>The specified value is not valid.</h3></div>

<div class="section" id="datetime:bad-year"><h3>Year number is out of range.</h3></div>

<div class="section" id="datetime:bad-month"><h3>Month number is out of range.</h3></div>

<div class="section" id="datetime:bad-day"><h3>Day number is out of range.</h3></div>

<div class="section" id="datetime:bad-hour"><h3>Hour number is out of range.</h3></div>

<div class="section" id="datetime:bad-minute"><h3>Minute number is out of range.</h3></div>

<div class="section" id="datetime:bad-second"><h3>Second number is out of range.</h3></div>

<div class="section" id="datetime:bad-timezone-hour"><h3>Hour number of the timezone component is out of
  range.</h3></div>

<div class="section" id="datetime:bad-timezone-minute"><h3>Minute number of the timezone component is out of
  range.</h3></div>

<div class="section" id="datetime:syntax-error"><h3>The value is not a datetime.</h3></div>

<div class="section" id="dateortime:syntax-error"><h3>The value is not a date or time.</h3></div>

<div class="section" id="empty-form-name"><h3>Form name is empty.</h3></div>

<div class="section" id="enumerated:invalid"><h3>This attribute only allow a limited set of 
  values and the specified value <code><var>{@}</var></code> is not one 
  of them.</h3>
    <p>For this attribute only several values are allowed and the
    value of the attribute is not one of them.  The document
    is non-conforming.</p>

    <dl>
    <dt>HTML <code>meta</code> element, <code>http-equiv</code> attribute</dt>
        <dd><p>Only values <code>Default-Style</code> and <code>Refresh</code>
        are allowed.</p>
        <p>Value <code>Content-Type</code> is obsolete; for charset
        declaration, the <code>charset</code> attribute can be used as:
        <pre class="html example">
<code>&lt;meta charset="<var>charset-name</var>"&gt;</code></pre>
        ... where <var>charset-name</var> is a name of the character encoding
        of the document, such as <code>utf-8</code>.</p>
        <p>Values <code>Content-Style-Type</code> and
        <code>Content-Script-Type</code> are currently not allowed.</p>
        <p>Value <code>Keywords</code> is not allowed.  Use
        <code>name</code> attribute instead of <code>http-equiv</code>
        attribute.</p>
        <p>Values <code>Expires</code>, <code>Pragma</code>,
        and <code>Cache-Control</code> are not allowed;
        use <em>real</em> HTTP header fields for cache control.</p></dd>
    </dl>
  </div>

<div class="section" id="enumerated:invalid:http-equiv:content-type"><h3>Character encoding declaration syntax
  <code class="html bad example">&lt;meta http-equiv="Content-Type" content="text/html; charset=<var>charset-name</var>"&gt;</code>
  is obsolete.</h3>
    <p>Old long character encoding declaration syntax
    <code class="html bad example">&lt;meta http-equiv="Content-Type" content="text/html; charset=<var>charset-name</var>"&gt;</code>
    is in use.  The document is non‐conforming.</p>

    <p>The new character encoding declaration syntax is:
      <pre class="html example">
<code>&lt;meta charset="<var>charset-name</var>"&gt;</code></pre>
    </p>
  </div>

<div class="section" id="enumerated:non-conforming"><h3>Attribute value <code><var>{@}</var></code>
  is not allowed.</h3></div>

<div class="section" id="duplicate-form-name"><h3>Form name <code><var>{value}</var></code> is already
  used for another element.</h3></div>

<div class="section" id="duplicate-http-equiv"><h3>There is another pragma
  <code><var>{value}</var></code>.</h3></div>

<div class="section" id="duplicate-ID"><h3>This identifier has already been
  assigned to another element.</h3></div>

<div class="section" id="duplicate-token"><h3>The token <code><var>{value}</var></code>
  appears in the attribute value twice.</h3></div>

<div class="section" id="empty-anchor-image-alt"><h3>The <code>alt</code> attribute value is 
  empty.</h3></div>

<div class="section" id="empty-area-alt"><h3>The <code>alt</code> attribute value is
  empty.</h3>
    <p>The value of the <code>alt</code> attribute of an <code>area</code>
    element is an empty value.</p>

    <p>In general, the <code>alt</code> attribute value cannot be empty.
    It must provide an alternative text for the hyperlink represented by
    the <code>area</code> element.  The alternative text is to be used
    when the Web browser cannot display the image, or is configured not
    to display images.</p>

    <p>As an exception, the <code>alt</code> attribute may be left blank
    if the same image map (i.e. the ancestor <code>map</code> element)
    contains another <code>area</code> element whose <code>href</code>
    attribute references the same resource as the <code>href</code>
    attribute of the <code>area</code> element in question, and the other
    <code>area</code> element has an <code>alt</code> attribute with
    non‐empty value.</p>
  </div>

<div class="section" id="empty-attribute-value"><h3>The attribute value is empty.</h3></div>

<div class="section" id="empty-style-sheet-title"><h3>The value of the <code>title</code> attribute
  is empty.</h3>
    <p>The <code>title</code> attribute value of the <code>link</code>
    element that defines an alternate style sheet is an empty value.</p>

    <p>A <code>link</code> element whose <code>rel</code> attribute
    is <code>alternate stylesheet</code> defines an alternate style sheet.
    An alternate style sheet must be associated with a name using the
    <code>title</code> attribute.  The name cannot be empty.</p>
  </div>

<div class="section" id="float:out-of-range"><h3>The specified value is out of range.</h3></div>

<div class="section" id="float:syntax-error"><h3>The attribute value is not a real
  number.</h3></div>

<div class="section" id="fragment-points-itself"><h3>A fragment identifier references the element
  itself.</h3></div>

<div class="section" id="fragment-points-nothing"><h3>A fragment identifier references no
  node.</h3></div>

<div class="section" id="hashref:syntax-error"><h3>A hash−name reference must start with a
  <code>#</code> character.</h3></div>

<div class="section" id="id-ne-name"><h3>The <code>id</code> attribute value is 
  different from the <code>name</code> attribute value.</h3></div>

<div class="section" id="integer:syntax-error"><h3>The attribute value is not an integer.</h3></div>

<div class="section" id="link-type:bad-context"><h3>The link type <code><var>{value}</var></code>
  cannot be specified for this element.</h3>
    <p>The specified link type cannot be used for the element.
    The document is non-conforming.</p>

    <p>Link types are associated with limited set of elements.
    They cannot be used with other elements.</p>

    <p>For example, link type <code>bookmark</code>
    can be used with <code>a</code> or <code>area</code> element,
    while it cannot be used with <code>link</code> element.</p>
  </div>

<div class="section" id="invalid-attribute-value"><h3>Attribute value <code><var>{@}</var></code>
  is not an allowed value.</h3></div>

<div class="section" id="length:syntax-error"><h3>The attribute value is not a length
  value.</h3></div>

<div class="section" id="link-type:non-conforming"><h3>The link type <code><var>{value}</var></code>
  is non-conforming.</h3>
    <p>The specified link type is non-conforming, and therefore
    the document is non-conforming.</p>

    <dl class="switch">
    <dt>Link type <code>contents</code></dt>
      <dd>Use link type <code>index</code>.</dd>
    <dt>Link type <code>copyright</code></dt>
      <dd>Use link type <code>license</code>.</dd>
    <dt>Link type <code>home</code></dt>
      <dd>Use link type <code>index</code>.</dd>
    <dt>Link type <code>previous</code></dt>
      <dd>Use link type <code>prev</code>.</dd>
    <dt>Link type <code>start</code></dt>
      <dd>Use link type <code>first</code>.</dd>
    <dt>Link type <code>toc</code> or <code>top</code></dt>
      <dd>Use link type <code>index</code>.</dd>
    </dl>
  </div>

<div class="section" id="meta-content-type-syntax-error"><h3>The specified value is not a valid as a long
  character encoding declaration.</h3></div>

<div class="section" id="mismatched-charset-name"><h3>The specified character encoding name
  <code><var>{value}</var></code> is different from the actual document
  character encoding <code><var>{text}</var></code>.</h3>
    <p>The specified character encoding name is different from
    the character encoding of the document.  The document
    is non‐conforming.</p>
  </div> 

<div class="section" id="mismatched-charset-name-not-checked"><h3>Whether the specified character encoding name
  <code><var>{value}</var></code> matches to the actual character encoding
  name cannot be checked since the input is not a byte stream.</h3></div>

<div class="section" id="mode:syntax-error"><h3>The attribute value is not a valid mode
  name.</h3></div>

<div class="section" id="nninteger:out-of-range"><h3>The specified value is out of range.</h3></div>

<div class="section" id="nninteger:syntax-error"><h3>The attribute value is not a non‐negative
  integer.</h3></div>

<div class="section" id="no-referenced-form"><h3>The element referneced by the <code>form</code>
  attribute is not a <code>form</code> element, or no element is
  found.</h3></div>

<div class="section" id="no-referenced-map"><h3>The element referneced by the <code>usemap</code>
  attribute is not a <code>map</code> element, or no element is
  found.</h3></div>

<div class="section" id="no-referenced-menu"><h3>The element referneced by the
  <code>contextmenu</code> attribute is not a <code>menu</code> element, or
  no element is found.</h3></div>

<div class="section" id="no-referenced-header-cell"><h3>There is no table header cell whose <code>id</code>
  is <code><var>{value}</var></code> in the same table.</h3></div>

<div class="section" id="refresh:syntax-error"><h3>the specified value is not a valid as part
  of a <code>Refresh</code> pragma.</h3></div>

<div class="section" id="repeat:syntax-error"><h3>The attribute value is not an integer or 
  a string <code>template</code>.</h3></div>

<div class="section" id="reserved-browsing-context-name"><h3>Browsing context name 
  <code><var>{@}</var></code> is reserved.</h3>
    <p>The specified browsing context name is reserved.
    The document is non-conforming.</p>

    <p>Names of browsing contexts starting with <code>_</code>
    (<code>U+005F</code> <code class="charname">LOW LINE</code>)
    are reserved so that it must not be used.</p>

    <p>Old version of HTML, non-HTML markup languages, and
    Web browsers define or implements special reserved
    browsing context names <code>_blank</code>,
    <code>_main</code>, and <code>_replace</code>.
    However, they are <em>not</em> conforming attribute values.</p>
  </div>

<div class="section" id="Reserved-Prefixes-and-Namespace-Names:Name"><h3>Namespace name <code><var>{text}</var></code>
  is reserved and cannot be used for an arbitrary prefix.</h3></div>

<div class="section" id="Reserved-Prefixes-and-Namespace-Names:Prefix"><h3>Namespace prefix <code><var>{text}</var></code>
  is reserved and cannot be used for an arbitrary namespace name.</h3></div>

<div class="section" id="link-type:proposed"><h3>Link type <code><var>{value}</var></code>
  is proposed but not accepted yet; it <em>should not</em> be
  used until it has been accepted.</h3>
    <p>The link type is in the <i>proposed</i> status; it
    <em>should not</em> be used until it has been
    accepted.</p>

    <p><strong>Warning</strong>: The data served to the
    conforming checker might be out of date; it might have already
    been accepted or rejected.  The document might or might not be
    conforming depending on the status.  See WHATWG Wiki
    for the latest information.</p>
  </div>

<div class="section" id="sizes:syntax-error"><h3>The specified value <code><var>{value}</var></code>
  is not a valid value.</h3></div>

<div class="section" id="space-in-ID"><h3>White space characters are not allowed
  in the <code>id</code> attribute.</h3></div>

<div class="section" id="template:not-template"><h3>The node referenced by the <code>template</code>
  attribute is not a template.</h3></div>

<div class="section" id="value-too-long"><h3>The <code>value</code> attribute value is longer
  than the value of the <code>maxlength</code> attribute.</h3></div>

<div class="section" id="window-name:empty"><h3>Browsing context name must not be empty.</h3></div>

<div class="section" id="window-name:reserved"><h3>Browsing context name
  <code><var>{value}</var></code> is reserved.</h3></div>

<div class="section" id="word-not-allowed"><h3>The word <code><var>{value}</var></code> is not
  allowed in this attribute.</h3></div>

<div class="section" id="XML-1.0-NCName:syntax-error"><h3>The specified value is not a legal XML Namespaces
  1.0 <code>NCName</code>.</h3></div>

<div class="section" id="xml:lang-ne-lang"><h3>The value of the <code>xml:lang</code> attribute
  is different from the value of the <code>lang</code> attribute.</h3>
    <p>The value of the <code>xml:lang</code> attribute (either the
    <code>lang</code> attribute in the <code>xml</code> (i.e.
    <code>http://www.w3.org/XML/1998/namespace</code>) namespace, or
    the <code>xml:lang</code> attribute in no namespace) for the element has
    different value than that of the <code>lang</code> attribute in no
    namespace.</p>

    <p>For historical reason, there are two attributes applicable to HTML
    elements to specify language information of an element: <code>lang</code>
    and <code>xml:lang</code>.  In HTML documents, only <code>lang</code>
    attribute in no namespace is allowed and take effect; the
    <code>xml:lang</code> attribute in no namespace is ignored in HTML
    documents.  In XHTML documents, both <code>lang</code> and
    <code>xml:lang</code> attributes are allowed.</p>

    <p>In general, <em>only the <code>lang</code> attribute</em> need to be
    specified for an element.</p>

    <p>If both <code>lang</code> and <code>xml:lang</code> attributes are
    specified on the same element, their values must be the same value.</p>
  </div>

</section>

<section id="table-model-errors">
<h2>Table Model Errors</h2>

<div class="section" id="cell-overlapping"><h3>Cell slot (<var>{text}</var>) is filled by
  multiple cells.</h3></div>

<div class="section" id="colspan-creates-column-with-no-anchored-cell"><h3>This <code>colspan</code> attribute
  results in creating a table column that does not contain
  any cell anchored to it.</h3></div>

<div class="section" id="column-with-no-anchored-cell"><h3>This column has no anchored cell.</h3></div>

<div class="section" id="table:no-cell-in-last-row"><h3>The table has no cell (<code>td</code> or
  <code>th</code>) in the last row.</h3></div>

<div class="section" id="table:rowspan-extends-table"><h3>This <code>rowspan</code> attribute
  results in creating a table row that does not contain
  any cell anchored to it.</h3>
    <p>The <code>rowspan</code> attribute value of the cell
    is so specified that it extends a table in the row axis.
    However, the extended row does not contain any cell by itself.
    The document is non-conforming.</p>

    <p>For example, the table below is non-conforming:
      <pre class="html bad example">
<code>&lt;table&gt;
&lt;tbody&gt;
&lt;tr&gt;&lt;td rowspan=2&gt;&lt;/td&gt;&lt;/tr&gt;
&lt;/tbody&gt;
&lt;/table&gt;</code></pre>
    ... since the second row contains only
    a cell that spans between first and second rows.</p>
  </div>

<div class="section" id="row-with-no-anchored-cell"><h3>This row has no anchored cell.</h3></div>

<div class="section" id="rowspan-creates-row-with-no-anchored-cell"><h3>This <code>rowspan</code> attribute
  results in creating a table row that does not contain
  any cell anchored to it.</h3></div>


</section>

<section id="imt-warnings">
<h2>Internet Media Type Errors</h2>

<div class="section" id="boundary:syntax-error"><h3>The specified value is not a valid value
  as a multipart boundary.</h3></div>

<div class="section" id="e4x:syntax-error"><h3>The specified value is not a valid value
  for the attribute <code>e4x</code>.</h3></div>

<div class="section" id="IMT:attribute-syntax-error"><h3>The specified value,
  <code><var>{value}</var></code>, is syntactically not a valid
  attribute name.</h3></div>

<div class="section" id="IMT:composite"><h3>The specified media type is a composite
  type, which is not allowed in this context.</h3></div>

<div class="section" id="IMT:limited-use-subtype"><h3>An Internet Media Type whose intended usage
  is limited use, <code><var>{value}</var></code> is used.</h3></div>

<div class="section" id="IMT:syntax-error"><h3>The specified value is not an Internet Media
  Type.</h3></div>

<div class="section" id="IMT:obsolete-parameter"><h3>An obsolete parameter
  <code><var>{value}</var></code> is used.</h3></div>

<div class="section" id="IMT:obsolete-subtype"><h3>An obsolete Internet Media Type
  <code><var>{value}</var></code> is used.</h3>
    <p>The specified Internet Media Type is registered with its intended
    usage as <i>OBSOLETE</i>.</p>
    
    <dl class="swtich">
    <dt>Media type <code>text/ecmascript</code></dt>
      <dd>Media type <code>text/ecmascript</code> is obsoleted in
      favor of <code>application/ecmascript</code>.  Note that
      <em><code>text/javascript</code></em> would be the better alternative
      in many cases.</dd>
    <dt>Media type <code>text/javascript</code></dt>
      <dd>Media type <code>text/javascript</code> is obsoleted by 
      <abbr>IETF</abbr> with backward incompatible alternate
      <code>application/javascript</code> for architectural 
      purity.<!-- @@ ref? -->  Those who prefer reality to academic
      purity <em>may ignore</em> this warning.</dd>
    </dl>
  </div>

<div class="section" id="IMT:parameter-missing"><h3>Parameter <code><var>{text}</var></code> have to
  be specified for the Internet Media Type
  <code><var>{value}</var></code>.</h3></div>

<div class="section" id="IMT:parameter-not-allowed"><h3>Parameter <code><var>{value}</var></code> is not
  allowed for this Internet Media Type.</h3></div>

<div class="section" id="IMT:private-subtype"><h3>Use of a private Internet Media Type
  <code><var>{value}</var></code> is not encouraged.</h3></div>

<div class="section" id="IMT:private-type"><h3>Use of a private type
  <code><var>{value}</var></code> is not encouraged.</h3></div>

<div class="section" id="IMT:subtype-syntax-error"><h3>Value <code><var>{value}</var></code> is
  syntactically not a valid subtype value of an Internet Media Type.</h3></div>

<div class="section" id="IMT:type-syntax-error"><h3>Value <code><var>{value}</var></code> is
  syntactically not a valid type.</h3></div>

<div class="section" id="IMT:unknown-parameter"><h3>An unknown parameter <code><var>{value}</var></code>
  is used.  The conformance checker cannot determine whether use of this
  parameter is valid or not.</h3></div>

<div class="section" id="IMT:unknown-subtype"><h3>An unknown Internet Media Type
  <code><var>{value}</var></code> is used.  At the time of the update of 
  the conformance checker's Internet Media Type database, the subtype is
  not reigstered to the IANA registry.  The subtype, however, might be
  registerd to the IANA registry thereafter.  Please consult the IANA
  registry.</h3></div>

<div class="section" id="IMT:unregistered-subtype"><h3>Use of an Internet Media Type
  <code><var>{value}</var></code> is not encouraged since it is not
  part of the IANA registry.</h3></div>

<div class="section" id="IMT:unregistered-type"><h3>Use of a type
  <code><var>{value}</var></code> is not encouraged since it is not
  a standardized type.</h3></div>

<div class="section" id="not-IMT"><h3>A value that is not an Internet Media Type
  is not allowed here.</h3></div>

</section>

<section id="uri-errors">
<h2>URL Errors</h2>

<div class="section" id="syntax-error:iri3987"><h3>The specified value is syntactically not an
  IRI.</h3></div>

<div class="section" id="syntax-error:iriref3987"><h3>The specified value is syntactically not an IRI
  reference.</h3>
    <p>The specified value does not satisfy the syntactical requirements
    for IRI references.  The document is non-conforming.</p>

    <p>Possible causes:
      <ul>
      <li>The string might contain one or more white space characters.
      Especially, the <code> </code> (<code>U+0020</code>
      <code class="charname">SPACE</code>) character cannot be
      used in IRI references.</li>
      </ul>
    </p>
  </div>

<div class="section" id="syntax-error:rdfuriref"><h3>The specified value is syntactically not an RDF
  URI reference.</h3></div>

<div class="section" id="syntax-error:uri2396"><h3>The specified value is syntactically not a
  URI according to RFC 2396.</h3></div>

<div class="section" id="syntax-error:uri3986"><h3>The specified value is syntactically not a
  URI.</h3></div>

<div class="section" id="URL:address-format"><h3>URL host address format
  <code><var>{text}</var></code> is not defined.</h3></div>

<div class="section" id="URL:default-port"><h3>Default port number should be omitted.</h3></div>

<div class="section" id="URL:dot-segment"><h3>A dot-segment (<code>.</code> or
  <code>..</code>) occurs in an absolute reference.</h3>
    <p>Dot-segment (<code>.</code> or <code>..</code>) should
    not occur in an absolute reference.</p>

    <p>In relative references, dot-segments are used to represent
    the current (<code>.</code>) or the parent (<code>..</code>) 
    hierarchy of the path.  Though they are also allowed
    in absolute references, it should be resolved to the
    canonical form before it has been published.</p>
  </div>

<div class="section" id="URL:empty-host"><h3>The host component of the URL is empty.</h3></div>

<div class="section" id="URL:empty-path"><h3>The URL does not end with
  a <code>/</code> character.</h3></div>

<div class="section" id="URL:empty-port"><h3>The port component of the URL is empty.</h3></div>

<div class="section" id="URL-fragment-not-allowed"><h3>The fragment component of the URL is not 
  allowed.</h3></div>

<div class="section" id="URL:long-host"><h3>The host component of the URL
  is too long.</h3></div>

<div class="section" id="URL:lowercase-hexadecimal-digit"><h3>A lowercase hexadecimal digit is used
  in percent-encoding.</h3>
    <p>The hexadecimal digit in percent-encoding string in the IRI
    is in lowercase.  Though the IRI <em>is</em> conforming,
    it should be in uppercase.</p>
  </div>

<div class="section" id="URL:non-DNS-host"><h3>The host component of the URL
  is not a DNS host name.</h3></div>

<div class="section" id="URL:non-UTF-8-host"><h3>The host component of the URL
  is not encoded in UTF-8.</h3></div>

<div class="section" id="URL:password"><h3>Password should not be included in a URL
  for the security.</h3></div>

<div class="section" id="URL:percent-encoded-unreserved"><h3>An unreserved character is 
  percent-encoded.</h3>
    <p>An unreserved character is percent-encoded in the IRI.
    Though it <em>is</em> conforming, it should be in the 
    decoded (or bare) form.</p>
  </div>

<div class="section" id="URL:uppercase-host"><h3>The host <code><var>{value}</var></code>
  should be spelt in lowercase.</h3></div>

<div class="section" id="URL:uppercase-scheme-name"><h3>URL scheme name is in uppercase.</h3>
    <p>The scheme part of the IRI is written in uppercase letter.</p>

    <p>Uppercase scheme names are not required to be processed
    correctly.</p>
<!-- @@
 RFC 3986 3.1.
 > Although schemes are case-
   insensitive, the canonical form is lowercase and documents that
   specify schemes must do so with lowercase letters.
 
 > An implementation ... should only produce lowercase scheme names for
   consistency.
-->
  </div>

</section>

<section id="mq-errors">
<h2>Media Query Errors</h2>

<div class="section" id="mq-syntax-error"><h3>The specified value has a syntax error as a
  media query.</h3></div>

<div class="section" id="unknown-media-type"><h3>Media type <code><var>{value}</var></code> is
  not supported by the conformance checker.</h3></div>

</section>

<section id="selectors-errors">
<h2>Selectors Errors</h2>

<div class="section" id="an+b-not-closed"><h3>Argument list of the pseudo-class is
  not closed by a <code>)</code> character.</h3></div>

<div class="section" id="ab+b-not-integer"><h3>Numbers in the argument
  <code><var>a</var>n+<var>b</var></code> have to be integers.</h3></div>

<div class="section" id="an+b-syntax-error"><h3>Argument <code><var>a</var>n+<var>b</var></code> is 
  syntactically incorrect.</h3></div>

<div class="section" id="attr-selector-not-closed"><h3>Attribute selector is not closed by
  a <code>]</code> character.</h3></div>

<div class="section" id="lang-selector-not-closed"><h3>Argument list of the <code>:lang</code>
  selector is not closed by a <code>)</code> character.</h3></div>

<div class="section" id="namespace-prefix:not-declared"><h3>Namespace prefix <code><var>{value}</var></code>
  is not declared.</h3></div>

<div class="section" id="no-attr-local-name"><h3>Attribute local name is missing.</h3></div>

<div class="section" id="no-attr-match"><h3>Attribute matching operator (e.g.
  <code>=</code>) is missing.</h3></div>

<div class="section" id="no-attr-name"><h3>Attribute name is missing.</h3></div>

<div class="section" id="no-attr-namespace-separator"><h3>Attribute namespace wildcard <code>*</code>
  is not followed by a <code>|</code> character.</h3></div>

<div class="section" id="no-attr-value"><h3>Attribute value is missing.</h3></div>

<div class="section" id="no-class-name-selector"><h3>Class name is missing.</h3></div>

<div class="section" id="no-combinator"><h3>Combinator is missing.</h3></div>

<div class="section" id="no-contains-string"><h3>No string is specified in the argument
  list of the <code>:-manakai-contains</code> pseudo-class
  selector.</h3></div>

<div class="section" id="no-lang-tag"><h3>Language tag argument is missing.</h3></div>

<div class="section" id="no-local-name-selector"><h3>Local name part of the type selector (or 
  <code>*</code> for the universal selector) is missing.</h3></div>

<div class="section" id="no-pseudo-class-name"><h3>Pseudo-class name is missing.</h3></div>

<div class="section" id="no-pseudo-element-name"><h3>Pseudo-element name is missing.</h3></div>

<div class="section" id="no-sss"><h3>Sequence of simple selectors is
  expected.</h3></div>

<div class="section" id="not-not-closed"><h3>Argument list of the <code>:not</code> selector
  is not closed by a <code>)</code> character.</h3></div>

<div class="section" id="ss-after-pseudo-element"><h3>Simple selector is not allowed after a
  pseudo element.</h3></div>

<div class="section" id="unknown-pseudo-class"><h3>Pseudo-class <code>:<var>{value}</var></code>
  is not supported by the conformance checker.</h3></div>

<div class="section" id="unknown-pseudo-element"><h3>Pseudo-element <code>::<var>{value}</var></code>
  is not supported by the conformance checker.</h3></div>

</section>

<section id="css-errors">
<h2>CSS Errors</h2>

<div class="section" id="at-rule-not-allowed"><h3>An <code>@<var>{text}</var></code> rule is not
  allowed here.</h3></div>

<div class="section" id="at-rule-syntax-error"><h3>The <code>@<var>{text}</var></code> rule is
  syntactically incorrect.</h3></div>

<div class="section" id="block-not-closed"><h3>Block is not closed before the end of
  file.</h3></div>

<div class="section" id="CSS-duplication"><h3>Component <code>&lt;<var>{text}</var>&gt;</code> is
  already specified.</h3></div>

<div class="section" id="CSS-cursor-hand"><h3>Value <code>hand</code> is not valid as
  <code>&lt;'cursor'&gt;</code>.</h3></div>

<div class="section" id="CSS-syntax-error"><h3>Specified value is syntactically not a correct
  <code>&lt;<var>{text}</var>&gt;</code>.</h3></div>

<div class="section" id="no-declaration-block"><h3>No declaration block is found after a group of
  selectors.</h3></div>

<div class="section" id="no-property-colon"><h3>A <code>:</code> character is missing after
  a property name.</h3></div>

<div class="section" id="no-property-name"><h3>Property name is expected.</h3></div>

<div class="section" id="no-property-semicolon"><h3>A <code>;</code> character is missing at the
  end of the property.</h3></div>

<div class="section" id="priority-syntax-error"><h3>Priority part of the declaration is syntactically
  incorrect.</h3></div>

<div class="section" id="unknown-at-rule"><h3>The <code>@<var>{value}</var></code> rule is
  not supported by the conformance checker.</h3></div>

<div class="section" id="unknown-property"><h3>Property <code><var>{value}</var></code> is
  not supported by the conformance checker.</h3></div>

</section>

<section id="cache-manifest-errors">
<h2>Cache Manifest Errors</h2>

<div class="section" id="both-in-entries-and-whitelist"><h3>This URL is found both in the explicit or
  fallback entries and in the online whitelist.</h3></div>

<div class="section" id="different-origin-from-manifest"><h3>The specified URL has different origin from
  the manifest.</h3></div>

<div class="section" id="different-scheme-from-manifest"><h3>The scheme component of the URL is
  different from that of the manifest URL.  The URL is ignored.</h3></div>

<div class="section" id="duplicate-oc-namespace"><h3>This oppotunistic caching namespace is already
  specified.</h3></div>

<div class="section" id="no-fallback-entry-URL"><h3>Fallback entry URL is missing.</h3></div>

<div class="section" id="not-manifest"><h3>This document is not a cache manifest.</h3>
    <p>The specified document is <em>not</em> a cache manifest.
    The document is non-conforming.</p>

    <p>An entity labeled as Internet media type 
    <code>text/cache-manifest</code> must contain a cache manifest.</p>

    <p>A cache manifest must start with a line whose content is 
    <code class="manifest example">CACHE MANIFEST</code>
    (exactly one space character between
    <code>CACHE</code> and <code>MANIFEST</code>).</p>
  </div>

<div class="section" id="same-as-manifest-URL"><h3>This URL is same as the manifest URL.</h3></div>

</section>

<section id="regexp-errors">
<h2>Regular Expression Errors</h2>

<!-- Errors in this section are sorted by
Regexp::Parser::Diagnostics's order, then followed by the
Regexp::Parser::JavaScript's extension. -->

<!-- TODO: mark fatal errors as such -->

<div class="section" id="Quantifier-unexpected-on-zero-length-expression"><h3>Quantifier unexpected on zero-length
  expression.</h3></div>

<div class="section" id="Sequence-(?%.*s...)-not-implemented"><h3>Sequence
  <code>(?<var>{text}</var><var>...</var>)</code> is not implemented
  by Perl.</h3></div>

<div class="section" id="Sequence-(?#...-not-terminated"><h3>Sequence <code>(?#<var>...</var></code> is
  not terminated by <code>)</code>.</h3></div>

<div class="section" id="(?p{})-is-deprecated----use-(??{})"><h3><code>(?p{<var>...</var>})</code> is
  obsolete.</h3>
    <p><code>(?p{})</code> is obsolete.  It was deprecated in
    Perl 5.8 and is <em>no longer supported</em> in Perl 5.10.</p>

    <p>You can use <code>(??{<var>...</var>})</code> instead.</p>
  </div>

<div class="section" id="Sequence-(?{...})-not-terminated-or-not-{}-balanced"><h3>Sequence <code>(?{<var>...</var>})</code>
  is not terminated or <code>{<var>...</var>}</code> is not
  balanced.</h3></div>

<div class="section" id="Switch-condition-not-recognized"><h3>Switch condition is not recognized.</h3></div>

<div class="section" id="Switch-(?(condition)...-contains-too-many-branches"><h3>Switch
  <code>(?(<var>condition</var>)<var>...</var>|<var>...</var><mark>|...</mark>)</code>
  contains too many branches.</h3></div>

<div class="section" id="Unknown-switch-condition-(?(%.2s"><h3>An unknown switch condition
  <code>(?(<var>{text}</var></code> is used.</h3></div>

<div class="section" id="Sequence-(?-incomplete"><h3>Sequence <code>(?<var>...</var></code> is
  incomplete.</h3></div>

<div class="section" id="Useless-(?%s%s)----%suse-/%s-modifier"><h3>Modifier <code>(?<var>{text}</var>)</code>
  <em>in</em> a regular expression has no effect.</h3></div>

<div class="section" id="Sequence-(?%.*s...)-not-recognized"><h3>An unknown sequence
  <code>(?<var>{text}</var><var>...</var>)</code> is used.</h3></div>

<div class="section" id="Unmatched-("><h3>A <code>(<var>...</var></code> sequence
  is not terminated by <code>)</code>.</h3></div>

<div class="section" id="Unmatched-)"><h3>An unmatched <code>)</code> is found.</h3></div>

<div class="section" id="Can't-do-{n,m}-with-n-&gt;-m"><h3>Quantifier <code>{<var>n</var>,<var>m</var>}</code>
  cannot be <span class="math"><var>n</var> &gt; <var>m</var></span>.</h3></div>

<div class="section" id="%s-matches-null-string-many-times"><h3><code><var>{text}</var></code> matches
  the empty string too many times.</h3></div>

<div class="section" id="Nested-quantifiers"><h3>Quantifiers cannot be nested.</h3></div>

<div class="section" id="Unmatched-["><h3>A character class <code>[<var>...</var></code>
  is not terminated by <code>]</code>.</h3></div>

<div class="section" id="Quantifier-follows-nothing"><h3>Quantifier follows nothing.</h3></div>

<div class="section" id="Missing-braces-on-\%s{}"><h3>A <code>\<var>{text}</var></code> sequence
  is not followed by <code>{<var>...</var>}</code>.</h3></div>

<div class="section" id="Missing-right-brace-on-\%s{}"><h3>A <code>\<var>{text}</var>{<var>...</var></code>
  is not terminated by <code>}</code>.</h3></div>

<div class="section" id="Reference-to-nonexistent-group"><h3>A nonexistent group is referenced.</h3></div>

<div class="section" id="Trailing-\"><h3>A <code>\</code> character is not followed by
  another character,</h3></div>

<div class="section" id="Unrecognized-escape-\%s-passed-through"><h3>An unknown escape <code>\<var>{text}</var></code>
  is used.</h3></div>

<div class="section" id="Unrecognized-escape-\%s-in-character-class-passed-through"><h3>An unknown escape <code>\<var>{text}</var></code>
  is used in a character class.</h3></div>

<div class="section" id="POSIX-class-[:%s:]-unknown"><h3>An unknown POSIX character class
  <code>[:<var>{text}</var>:]</code> is used.</h3></div>

<div class="section" id="POSIX-syntax-[%s-%s]-belongs-inside-character-classes"><h3>A POSIX syntax
  <code>[<var>{text}</var><var>...</var><var>{text}</var>]</code> is used
  outside of character classes.</h3></div>

<div class="section" id="Empty-\%s{}"><h3>An escape <code>\<var>{text}</var>{}</code>
  is empty.</h3></div>

<div class="section" id="False-[]-range-&quot;%s-%s&quot;"><h3>An escape that represents a character
  class cannot be used in range <code><var>{text}</var></code>.</h3></div>

<div class="section" id="Invalid-[]-range-&quot;%s-%s&quot;"><h3>Character range <code><var>{text}</var></code>
  is invalid.</h3></div>

<div class="section" id="Octal-escape-is-obsolete"><h3>Octal escape is used.</h3></div>

</section>

<section id="webidl-errors">
<h2>WebIDL Errors</h2>

<div class="section" id="after-argument"><h3>An argument name is not followed by a
  <code>,</code> character or a <code>)</code> character.</h3></div>

<div class="section" id="after-exception-name"><h3>An exception name is not followed by a
  <code>,</code> character or a <code>)</code> character.</h3></div>

<div class="section" id="after-unsigned"><h3>キーワード <code>unsigned</code> の後の字句が
  <code>short</code> か <code>long</code> ではありません。</h3></div>

<div class="section" id="after-xattr"><h3>An extended attribute is not followed by 
  a <code>,</code> character or a <code>]</code> character.</h3></div>

<div class="section" id="argument-after-variadic"><h3>An argument is specified after an argument
  with <code>Variadic</code> extended attribute is seen.</h3></div>

<div class="section" id="attr-not-readonly"><h3>Extended attribute <code><var>{text}</var></code> is
  specified for an attribute that is not read-only.</h3></div>

<div class="section" id="attr-type-not-interface"><h3>Extended attribute <code><var>{text}</var></code>
  is specified for an attribute whose type is not an interface.</h3></div>

<div class="section" id="before-exception-member"><h3>An unknown construct is found where an exception
  member or a <code>}</code> character is expected.</h3></div>

<div class="section" id="before-interface-member"><h3>An unknown construct is found where an interface
  member or a <code>}</code> character is expected.</h3></div>

<div class="section" id="before-webidl-block"><h3>An identifier for the <code><var>{text}</var></code>
  is not followed by a <code>{</code> character.</h3></div>

<div class="section" id="before-webidl-def"><h3>An unknown construct is found after an
  extended attribute list (where a <code>Definition</code> is
  expected).</h3></div>

<div class="section" id="before-webidl-defs"><h3>An unknown construct is found where a
  <code>Definition</code> (optionally preceded by an extended attribute list)
  is expected.</h3></div>

<div class="section" id="before-webidl-type"><h3>The type for <code><var>{text}</var></code> is
  not specified.</h3></div>

<div class="section" id="before-webidl-type:argument"><h3>The type for an argument is not
  specified.</h3></div>

<div class="section" id="before-webidl-type:exception-member"><h3>The type for an exception member is not
  specified.</h3></div>

<div class="section" id="before-xattr"><h3>No extended attribute is specified after
  a <code>[</code> character.</h3></div>

<div class="section" id="before-xattrarg"><h3>No identifier is specified in an extended 
  attribute assignment.</h3></div>

<div class="section" id="const-value-out-of-range"><h3>The specified value <code><var>{value}</var></code>
  is outside of the range of the type for the constant,
  <code><var>{text}</var></code>.</h3></div>

<div class="section" id="const-type-mismatch"><h3>The type of the value,
  <code><var>{value}</var></code>, is different from the type of the constant,
  <code><var>{text}</var></code>.</h3></div>

<div class="section" id="duplicate-accessor"><h3>Extended attribute <code><var>{text}</var></code>
  is already specified for another operation in the same interface.</h3></div>

<div class="section" id="duplicate-constructor-name"><h3>Constructor name <code><var>{value}</var></code>
  specified by extended attribute <code><var>{text}</var></code> is already
  used for an interface.</h3></div>

<div class="section" id="duplicate-member"><h3>Name <code><var>{text}</var></code> is
  already used.</h3></div>

<div class="section" id="duplicate-qname"><h3>Qualified name <code><var>{text}</var></code> is
  already used.</h3></div>

<div class="section" id="duplicate-xattr"><h3>Extended attribute <code><var>{text}</var></code>
  is already specified.</h3></div>

<div class="section" id="exception-not-defined"><h3>Exception <code><var>{text}</var></code> is
  not defined in the fragment.</h3></div>

<div class="section" id="interface-not-defined"><h3>Interface <code><var>{text}</var></code> is
  not defined in the fragment.</h3></div>

<div class="section" id="no-arguments-in"><h3>No <code>in</code> keyword for an argument is
  found.</h3></div>

<div class="section" id="no-arguments-lparen"><h3>No <code>(</code> character for an argument
  list is found.</h3></div>

<div class="section" id="no-raises-lparen"><h3>A <code>raises</code> (or <code>getraises</code>
  or <code>setraises</code>) keyword is not followed by a <code>(</code>
  character.</h3></div>

<div class="section" id="no-sequence-gt"><h3>A <code>sequence&lt;&gt;</code> type is not
  terminated by a <code>&gt;</code> character.</h3></div>

<div class="section" id="no-sequence-lt"><h3>Keyword <code>sequence</code> is not followed
  by a <code>&lt;</code> character.</h3></div>

<div class="section" id="no-sequence-type"><h3>No type is specified in
  <code>sequence&lt;&gt;</code>.</h3></div>

<div class="section" id="no-webidl-identifier"><h3>No identifier is specified for the
  <code><var>{text}</var></code>.</h3></div>

<div class="section" id="no-webidl-identifier:argument"><h3>No identifier is specified for the
  argument.</h3></div>

<div class="section" id="no-webidl-identifier:exception-member"><h3>No identifier is specified for the
  exception member.</h3></div>

<div class="section" id="no-webidl-identifier:operation"><h3>No identifier is specified for the
  operation.</h3></div>

<div class="section" id="no-webidl-semicolon"><h3>No semicolon is found at the end of the
  definition or member.</h3></div>

<div class="section" id="non-module-definition"><h3>This definition is not part of any
  module.</h3></div>

<div class="section" id="not-boxable-type"><h3>Type <code><var>{text}</var></code> cannot be
  used in <code>valuetype</code>.</h3></div>

<div class="section" id="premature-end-of-webidl"><h3>The WebIDL fragment ends before all the blocks
  are closed by <code>};</code> sequences.</h3></div>

<div class="section" id="referenced-attr-not-defined"><h3>Attribute <code><var>{value}</var></code> is
  not defined in the interface specified for the attribute to which
  extended attribute <code><var>{text}</var></code> is set.</h3></div>

<div class="section" id="scoped-name"><h3>A scoped name is expected here.</h3></div>

<div class="section" id="scoped-name:dcolon"><h3>A <code>::</code> token is not followed by
  an identifier or a <code>DOMString</code> keyword.</h3></div>

<div class="section" id="type-not-defined"><h3>Type <code><var>{text}</var></code> is not 
  defined.</h3></div>

<div class="section" id="typedef-ignored"><h3><code>typedef</code> of name <code>DOMString</code>
  is ignored.</h3></div>

<div class="section" id="unknown-xattr"><h3>An unknown extended attribute 
  <code><var>{text}</var></code> is used.</h3></div>

<div class="section" id="valuetype-DOMString"><h3>The <code>valuetype</code> definition does
  not define <code>DOMString</code> as
  <code>sequence&lt;unsigned short&gt;</code>.</h3></div>

<div class="section" id="valuetype-ignored"><h3><code>valuetype</code> of name
  <code>DOMString</code> is ignored.</h3></div>

<div class="section" id="wrong-signature-accessor"><h3>The operation cannot be used as accessor operation
  of <code><var>{text}</var></code>, since its signature different from
  the expected one.</h3></div>

<div class="section" id="xattr-arglist-not-allowed"><h3>Use of an argument list for extended attribute
  <code><var>{text}</var></code> is not allowed.</h3></div>

<div class="section" id="xattr-for-wrong-type"><h3>Extended attribute <code><var>{text}</var></code>
  is not applicable for an attribute whose type is not
  <code>DOMString</code>.</h3></div>

<div class="section" id="xattr-id-missing"><h3>The identifier for extended attribute
  <code><var>{text}</var></code> is not specified.</h3></div>

<div class="section" id="xattr-id-not-allowed"><h3>Use of an identifier for extended attribute
  <code><var>{text}</var></code> is not allowed.</h3></div>

<div class="section" id="xattr-id-value-not-allowed"><h3>The identifier <code><var>{value}</var></code> is
  not an allowed value for extended attribute
  <code><var>{text}</var></code>.</h3></div>

<div class="section" id="xattr-not-applicable"><h3>Extended attribute <code><var>{text}</var></code>
  is not applicable to this kind of object.</h3></div>

</section>

<section id="information">
<h2>Stability Information</h2>

<div class="section" id="deprecated:attr"><h3>This attribute is deprecated.</h3></div>

<div class="section" id="deprecated:element"><h3>This element is deprecated.</h3></div>

<div class="section" id="status:cr:element"><h3>This element is in the
  <strong>call for implementation</strong> stage.</h3>
    <p>The element is in the call for implementation stage.</p>
    
    <p>Usually, using the element is safe.  However, it is a new feature
    so that it might not be implemented correctly.  If it is found that
    the feature is hard or impossible to implement, the feature
    might be revised, or in some case it might be dropped.</p>

    <p>Elements defined by Atom 1.0 (IETF Proposed Standard), and XBL 2.0
    (W3C Candidate Recommendation) belong to this class.</p>
  </div>

<div class="section" id="status:lc:element"><h3>This element is in the <strong>last
  call for comments</strong> stage.</h3>
    <p>The element is in the last call for comments stage.</p>
    
    <p>The element is relatively mature, though the standardization
    is not done yet.  It may be used for experiments.  Since it is a new
    feature, it might not be implemented correctly or at all.  If it is
    found that the feature is hard or impossible to implement, the feature
    might be revised or might be dropped.</p>

    <p>Elements defined by Web Forms 2.0 as well as some elements
    defined by HTML5 belong to this class.</p>
  </div>

<div class="section" id="status:wd:element"><h3>This element is documented in a <strong>working
  draft</strong>.</h3>
    <p>The element is documented in a working or editor's draft
    and not yet completed.</p>
    
    <p>The element should not be used for any practical purpose.
    The feature might be drastically changed later or might be
    entirely removed.</p>

    <p>Most of new elements defined by HTML5 belong to this class.</p>
  </div>

<div class="section" id="status:non-standard:element"><h3>This element is <strong>not part of any
  standard</strong> the conformance checker knows.</h3>
    <p>The element is not part of any standard or draft the conformance
    checker is aware of.</p>
    
    <p>The element should not be used for any practical purpose unless
    there is really a standard that defines the element.</p>
  </div>

<div class="section" id="status:cr:attr"><h3>This attribute is in the
  <strong>call for implementation</strong> stage.</h3>
    <p>The attribute is in the call for implementation stage.</p>
    
    <p>Usually, using the attribute is safe.  However, it is a new feature
    so that it might not be implemented correctly.  If it is found that
    the feature is hard or impossible to implement, the feature
    might be revised, or in some case it might be dropped.</p>
  </div>

<div class="section" id="status:lc:attr"><h3>This attribute is in the <strong>last
  call for comments</strong> stage.</h3>
    <p>The attribute is in the last call for comments stage.</p>
    
    <p>The attribute is relatively mature, though the standardization
    is not done yet.  It may be used for experiments.  Since it is a new
    feature, it might not be implemented correctly or at all.  If it is
    found that the feature is hard or impossible to implement, the feature
    might be revised or might be dropped.</p>
  </div>

<div class="section" id="status:wd:attr"><h3>This attribute is documented in a <strong>working
  draft</strong>.</h3>
    <p>The attribute is documented in a working or editor's draft
    and not yet completed.</p>
    
    <p>The attribute should not be used for any practical purpose.
    The feature might be drastically changed later or might be
    entirely removed.</p>
  </div>

<div class="section" id="status:non-standard:attr"><h3>This attribute is <strong>not part of any
  standard</strong> the conformance checker knows.</h3>
    <p>The attribute is not part of any standard or draft the conformance
    checker is aware of.</p>
    
    <p>The attribute should not be used for any practical purpose unless
    there is really a standard that defines the attribute.</p>
  </div>
</section>

<section id="langtag-errors">
<h2>Language Tag Errors</h2>

<div class="section" id="langtag:extension:duplication"><h3>There is another extension subtag
  <code><var>{value}</var></code>.</h3></div>

<div class="section" id="langtag:extension:order"><h3>Extension subtag <code><var>{value}</var></code>
  is placed after subtag <code><var>{text}</var></code>.</h3></div>

<div class="section" id="langtag:extension:unknown"><h3>Extension <code><var>{value}</var></code> is not
  defined when the conformance checker is written.</h3></div>

<div class="section" id="langtag:extlang:case"><h3>Extended language subtag
  <code><var>{value}</var></code> is not in the preferred form, i.e. in 
  lowercase.</h3></div>

<div class="section" id="langtag:extlang:deprecated"><h3>Use of extended language subtag
  <code><var>{value}</var></code> is deprecated<!-- in favor of {text} (might
  be undef) -->.</h3></div>

<div class="section" id="langtag:extlang:prefix"><h3>Extended language subtag
  <code><var>{text}</var></code> is not allowed in the combination with this
  language (and extended language) subtag(s).</h3></div>

<div class="section" id="langtag:extlang:invalid"><h3>Extended language subtag 
  <code><var>{text}</var></code> is not registered.</h3></div>

<div class="section" id="langtag:grandfathered:case"><h3>Language tag <code><var>{value}</var></code> is
  not in the preferred case combination.</h3></div>

<div class="section" id="langtag:grandfathered:deprecated"><h3>Use of language tag
  <code><var>{value}</var></code> is deprecated<!-- in favor of {text} (might
  be undef) -->.</h3></div>

<div class="section" id="langtag:grandfathered:invalid"><h3>Language tag <code><var>{value}</var></code> is
  not a combination of RFC 4646 subtags and is not a registered grandfathered
  tag.</h3></div>

<div class="section" id="langtag:illegal"><h3>Subtag <code><var>{value}</var></code> is 
  syntactically invalid.</h3></div>

<div class="section" id="langtag:language:case"><h3>It is a good practice to represent ISO 639-1
  language code <code><var>{value}</var></code> in lowercase.</h3></div>

<div class="section" id="langtag:language:deprecated"><h3>Use of language subtag
  <code><var>{value}</var></code> is deprecated<!-- in favor of {text} (might
  be undef) -->.</h3></div>

<div class="section" id="langtag:language:invalid"><h3>Language subtag <code><var>{value}</var></code>
  is not registered.</h3></div>

<div class="section" id="langtag:language:mul"><h3>Langauge tag <code>mul</code> should not be
  used.</h3></div>

<div class="section" id="langtag:language:nosemantics"><h3>No semantics is defined for language subtag
  <code><var>{value}</var></code>.</h3></div>

<div class="section" id="langtag:language:private"><h3>Language subtag <code><var>{value}</var></code>
  is a private use code.</h3></div>

<div class="section" id="langtag:language:syntax"><h3>The language subtag <code><var>{value}</var></code>
  is syntactically invalid.</h3></div>

<div class="section" id="langtag:language:und"><h3>Langauge tag <code>und</code> should not be
  used.</h3></div>

<div class="section" id="langtag:private"><h3>It would be better if a private use language
  tag (<code><var>{value}</var></code>) is not used.</h3></div>

<div class="section" id="langtag:privateuse"><h3>Private use subtag <code><var>{value}</var></code>
  is used.</h3></div>

<div class="section" id="langtag:privateuse:case"><h3>Subtag <code><var>{value}</var></code> is not 
  represented in the preferred case format.</h3></div>

<div class="section" id="langtag:privateuse:syntax"><h3>Private use subtag <code><var>{value}</var></code>
  is syntactically invalid.</h3></div>

<div class="section" id="langtag:redundant:case"><h3>Language tag <code><var>{value}</var></code> is
  not in the preferred case combination.</h3></div>

<div class="section" id="langtag:redundant:deprecated"><h3>Use of language tag
  <code><var>{value}</var></code> is deprecated<!-- in favor of {text} (might
  be undef) -->.</h3></div>

<div class="section" id="langtag:region:case"><h3>It is a good practice to represent ISO 3166
  country code <code><var>{value}</var></code> in uppercase.</h3></div>

<div class="section" id="langtag:region:deprecated"><h3>Use of region subtag
  <code><var>{value}</var></code> is deprecated<!-- in favor of {text} (might
  be undef) -->.</h3></div>

<div class="section" id="langtag:region:nosemantics"><h3>No semantics is defined for region subtag
  <code><var>{value}</var></code>.</h3></div>

<div class="section" id="langtag:region:invalid"><h3>Region subtag <code><var>{value}</var></code>
  is not registered.</h3></div>

<div class="section" id="langtag:region:private"><h3>Use of private use country code
  <code><var>{value}</var></code> is not allowed.</h3></div>

<div class="section" id="langtag:script:case"><h3>Script subtag <code><var>{value}</var></code> is 
  not in the preferred form, i.e. titlecase.</h3></div>

<div class="section" id="langtag:script:deprecated"><h3>Use of script subtag
  <code><var>{value}</var></code> is deprecated<!-- in favor of {text} (might
  be undef) -->.</h3></div>

<div class="section" id="langtag:script:invalid"><h3>Script subtag <code><var>{value}</var></code>
  is not registered.</h3></div>

<div class="section" id="langtag:script:private"><h3>Script subtag <code><var>{value}</var></code>
  is a private use code.</h3></div>

<div class="section" id="langtag:script:suppress"><h3>Script subtag <code><var>{value}</var></code>
  should be suppressed when the language subtag is
  <code><var>{text}</var></code>.</h3></div>

<div class="section" id="langtag:variant:case"><h3>Variant subtag <code><var>{value}</var></code> is
  not in the preferred form, i.e. lowercase.</h3></div>

<div class="section" id="langtag:variant:combination"><h3>Variant subtag <code><var>{text}</var></code> might
  not be meaningful when it is used in combination with
  <code><var>{value}</var></code>.</h3></div>

<div class="section" id="langtag:variant:deprecated"><h3>Use of variant subtag
  <code><var>{value}</var></code> is deprecated<!-- in favor of {text} (might
  be undef) -->.</h3></div>

<div class="section" id="langtag:variant:duplication"><h3>Variant subtag <code><var>{value}</var></code>
  is specified twice.</h3></div>

<div class="section" id="langtag:variant:invalid"><h3>Variant subtag <code><var>{value}</var></code>
  is not registered.</h3></div>

<div class="section" id="langtag:variant:prefix"><h3>Variant subtag <code><var>{value}</var></code>
  cannot be used in this context.</h3></div>

</section>

<section id="rdfxml-errors">
<h2>RDF/XML Errors</h2>

<div class="section" id="bad-rdf-namespace"><h3>The namespace URI of an element that
  represents an RDF concept must be 
  <code>http://www.w3.org/1999/02/22-rdf-syntax-ns#</code>.</h3></div>

<div class="section" id="duplicate-rdf-id"><h3>The specified value is already used as an
  ID.</h3></div>

<div class="section" id="duplicate-unqualified-attr"><h3>Both unqualified attribute and namespace‐qualified
  RDF attribute are specified, which is not allowed.</h3></div>

<div class="section" id="parse-type-other"><h3>An invalid value is specified to 
  the <code>parseType</code> attribute.</h3></div>

<div class="section" id="second-node-element"><h3>There is another element, such that
  this element is not allowed.</h3></div>

<div class="section" id="unqualified-attr"><h3>Unqualified attribute is not allowed.</h3></div>

<div class="section" id="unqualified-rdf-attr"><h3>RDF attribute should be
  namespace‐qualified.</h3></div>

</section>

<section id="unsupported-messages">
<h2><i>Unsupported</i> Messages</h2>

<div class="section" id="unknown-element"><h3>Conformance checking for element
  <code><var>{local-name}</var></code> is not supported; <em>it might or
  might not be conforming</em>.</h3>
    <p>The conformant checker does not support the element.
    It cannot determine whether the document is conforming or not.</p>
  </div>

<div class="section" id="unknown-attribute"><h3>Conformance checking for attribute
  <code><var>{local-name}</var></code> of element 
  <code><var>{element-local-name}</var></code> is not supported;
  <em>it might or might not be conforming</em>.</h3>
    <p>The conformant checker does not support the attribute.
    It cannot determine whether the document is conforming or not.</p>
  </div>

<div class="section" id="unknown-link-type"><h3>Link type <code><var>{value}</var></code> is not
  standardized or registered at the time of the release of the conformance
  checker; <em>it is non-conforming unless it now has been
  registered</em>.</h3>
    <p>The <code>rel</code> attribute is defined as a list of link types.
    Some common link types are defined in the HTML5 specification.
    Additional link types can be registered to the WHATWG Wiki.
    use of any other link type is non-conforming.</p>

    <p>The specified link type is not part of the standard or registry
    when the database used by the conformance cheker is created.
    The link type might have been added to the registry since then.
    In such case it might be conforming.  Otherwise, the
    document is non-conforming.</p>

    <dl>
    <dt>Link types <code>shortcut icon</code></dt>
        <dd>Link type <code>shortcut</code> is not registered.
        Use only <code>icon</code> for linking to so-called favicon.</dd>
    </dl>
  </div>

<div class="section" id="event-handler"><h3>Conformance checking for event handler attribute
  is not supported; <em>it might or might not be conforming.</em></h3></div>

<div class="section" id="media-query"><h3>Conformance checking for media query
  is not supported; <em>it might or might not be conforming.</em></h3></div>

<div class="section" id="addr-spec-not-supported"><h3>Conformance checking for an <code>addr-spec</code>
  is not supported; <em>it might or might not be conforming.</em></h3></div>

<div class="section" id="XML-script-lang"><h3>Conformance checking for script
  language <code><var>{text}</var></code> is not supported;
  <em>it might or might not be conforming.</em></h3></div>

<div class="section" id="XML-style-lang"><h3>Conformance checking for style
  language <code><var>{text}</var></code> is not supported;
  <em>it might or might not be conforming.</em></h3></div>

<div class="section" id="atom|content-not-supported"><h3>Conformance checking for an Atom
  <code>content</code> element with <code>type</code>
  <code><var>{text}</var></code> is not supported.</h3></div>

<div class="section" id="help-not-available"><h3>No more information is available.</h3>
    <p>No more information is available for this topic.</p>
  </div>

</section>


<div class="section" id="Error-level-m"><h3><a href="../error-description#Error-level-m" rel="help"><em class="rfc2119">MUST</em>‐level
        error</a></h3>
    <p>A violation to a hard requirement of the specification.
    The document is non‐conforming.</p>
  </div>

<div class="section" id="Error-level-s"><h3><a href="../error-description#Error-level-s" rel="help"><em class="rfc2119">SHOULD</em>‐level
        error</a></h3>
    <p>A violation to a requirement of the specification.
    The violation might be legitimize in some case.  Otherwise,
    the document is non‐conforming.</p>
  </div>

<div class="section" id="Error-level-w"><h3><a href="../error-description#Error-level-w" rel="help">Warning</a></h3>
    <p>A warning is an advice from the conformance checker
    to avoid solving a problem in a confusing or possibly wrong way.
    It does not affect to the conformance of the document, and
    may sometimes be inappropriate.</p>
  </div>

<div class="section" id="Error-level-i"><h3><a href="../error-description#Error-level-i" rel="help">Information</a></h3>
    <p>An informational message just provides an additional information
    on the feature used in the document or the status of the retrieval
    or so on.
    It does not affect to the conformance of the document.</p>
  </div>

<div class="section" id="Error-level-u"><h3><a href="../error-description#Error-level-u" rel="help">Not
      supported</a></h3>
    <p>Some feature that is not supported by the conformance checker
    is used in the document.</p>
  </div>

<section id="license">
<h2>License of This Document</h2>

<p>Copyright <time>2007</time>‐<time>2008</time>
<a href="http://suika.fam.cx/~wakaba/who?" rel="author" xml:lang="ja">Wakaba</a>
<code class="mail">&lt;<a href="mailto:w@suika.fam.cx">w@suika.fam.cx</a>&gt;</code>.</p>

<p>This document is free software; you can redistribute it
and/or modify it under the same terms as Perl itself.</p>
</section>

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