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

<!DOCTYPE html><html id="error-description" lang="en" xmlns:d="http://suika.fam.cx/~wakaba/archive/2007/wdcc-desc/" xmlns="http://www.w3.org/1999/xhtml">
<head>
<title xml:lang="en">Description of Errors — 
Web Document Conformance Checker (BETA)</title>
<link href="cc-style" rel="stylesheet">
<link href="#license" rel="license">
</head>
<body>
<h1>Description of Errors</h1>

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

<div class="section parse-error" id="after-html"><h3>Tag <code>&lt;<var>$0</var>&gt;</code>
  is not allowed after the end tag <code>&lt;/html&gt;</code>.</h3>
    <p>The start or end tag of an element appears after the
    <code>html</code> element has been closed.  The document is
    non-conforming.</p>

    <p>Any content of the document other than comments
    must be put into the <code>html</code> element.</p>
  </div>

<div class="section parse-error" id="after-body"><h3>Tag <code>&lt;<var>$0</var>&gt;</code>
  is not allowed after the end tag <code>&lt;/body&gt;</code>.</h3>
    <p>The start or 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 tokenize-error" id="bare-ero"><h3>The <code>&amp;</code> character must
  introduce a reference.</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 tokenize-error" 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 tokenize-error" 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 tokenize-error" 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 tokenize-error" 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 tokenize-error" 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 tokenize-error" 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 tokenize-error" 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 tokenize-error" id="duplicate-attribute"><h3>There are two attributes with name
      <code><var>$0</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 tokenize-error" 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 tokenize-error" id="pio"><h3>Processing instruction 
  (<code>&lt;?<var>...</var>&gt;</code>) cannot be used.</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=&quot;path/to/stylesheet.css&quot;&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>

</section>

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

<div class="section parse-error" id="after-head"><h3>The <code><var>$0</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 parse-error" id="DOCTYPE-in-the-middle"><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 parse-error" 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 parse-error" id="in-body"><h3>Tag <code>&lt;<var>$0</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 parse-error" 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 parse-error" id="in-table"><h3>Tag <code>&lt;<var>$0</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 parse-error" id="in-table:#character"><h3>Data character is not allowed in 
  <code>table</code>.</h3>
    <p>A data 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 parse-error" 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 parse-error" 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 parse-error" id="not-closed"><h3>Element <code><var>$0</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 parse-error" 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 parse-error" 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 parse-error" id="unmatched-end-tag"><h3>Element <code><var>$0</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>

</section>

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

<div class="section content-model-error" 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 content-model-error" id="child-element-missing"><h3>There must be a <code><var>$0</var></code>
  element 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 content-model-error" 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 content-model-error" 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 content-model-error" id="element-not-allowed:root"><h3>This element is not allowed as a root
  element.</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=&quot;http://www.w3.org/1999/xhtml&quot;&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=&quot;http://www.w3.org/2005/Atom&quot;&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 content-model-error" id="ps-element-missing"><h3>There is no <code><var>$0</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>

</section>

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

<div class="section attribute-error" id="attribute-missing"><h3>Required attribute <code><var>$0</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 attribute-error" 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 attribute-error" id="in-HTML:xml:lang"><h3>The <code>xml:lang</code> attribute is not 
  allowed in HTML document.</h3>
    <p>The <code>xml:lang</code> attribute is not allowed in
    HTML document.  The document is non-conforming.</p>

    <p>Use of the <code>xml:lang</code> attribute is conforming
    <em>only</em> in XML documents.</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 attribute-error" 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=&quot;1.0&quot; encoding=&quot;<var>encoding-name</var>&quot;?&gt;</code></pre>
    </p>
  </div>

<div class="section attribute-error" id="in-XML:lang"><h3>The <code>lang</code> attribute is not 
  allowed in XML document.</h3>
    <p>The HTML <code>lang</code> attribute is not allowed in
    XML document.  The document is non-conforming.</p>

    <p>The <code>lang</code> attribute in <code>null</code>
    namespace for HTML elements is conforming <em>only</em> in
    HTML documents.</p>

    <p>To specify natural language information in XML document,
    use <code>xml:lang</code> attribute instead.</p>
  </div>

<div class="section attribute-error" 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>

</section>

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

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

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

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

<div class="section attribute-value-error" id="link-type:bad-context"><h3>The link type <code><var>$0</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 attribute-value-error" id="link-type:non-conforming"><h3>The link type <code><var>$0</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 attribute-value-error" 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>

</section>

<section id="attribute-value-warnings">
<h2>Attribute Value Warnings</h2>

<div class="section attribute-value-warning should" id="s:link-type:proposed"><h3>Link type <code><var>$0</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>

</section>

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

<div class="section table-model-error" id="table: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 table-model-error" 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 table-model-error" 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>

</section>

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

<div class="section should" id="s:IMT:obsolete-subtype"><h3><code><var>{@}</var></code>: An <em>obsolete</em>
  subtype is used.</h3></div>

<div class="section should" id="s:IMT:private-subtype"><h3><code><var>{@}</var></code>: A private
  (<code>x-</code> or <code>x.</code>) subtype is used.</h3></div>

<div class="section should" id="s:IMT:unregistered-subtype"><h3><code><var>{@}</var></code>: The subtype is
  not registered to IANA.</h3></div>

</section>

<section id="uri-errors">
<h2>URI (or IRI) Errors</h2>

<div class="section must" id="m:URI::syntax-error"><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>

</section>

<section id="uri-shoulds">
<h2>URI (or IRI) Should-level Errors</h2>

<div class="section should" id="s:URI::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 should" id="s:URI::empty-path"><h3>This IRI does not end with
  a <code>/</code>.</h3></div>

<div class="section should" id="s:URI::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 should" id="s:URI::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 should" id="s:URI::uppercase-scheme-name"><h3>URI 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="cache-manifest-errors">
<h2>Cache Manifest Errors</h2>

<div class="section must" id="m: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>
</section>

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

<div class="section unsupported" id="unsupported: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 unsupported" id="unsupported: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 unsupported" id="unsupported:link-type"><h3>Link type <code><var>$0</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 unsupported" id="unsupported: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 unsupported" id="unsupported: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 unsupported" id="unsupported:script"><h3>Conformance checking for script
  language <code><var>$0</var></code> is not supported;
  <em>it might or might not be conforming.</em></h3></div>

<div class="section unsupported" id="unsupported:style"><h3>Conformance checking for style
  language <code><var>$0</var></code> is not supported;
  <em>it might or might not be conforming.</em></h3></div>

</section>


<section id="levels">
<h2>Error Levels</h2>

<table id="levels-table">
<thead>
<tr><th scope="col">Level</th>
<th scope="col">Conforming?</th>
<th scope="col">Description</th>
</tr>
</thead>
<tbody>
<tr class="level-m" id="level-m">
<th scope="row"><em class="rfc2119">MUST</em>‐level error</th>
<td>Non‐conforming.</td>
<td>A violation to a hard requirement of the specification.
The document is non‐conforming.</td>
</tr>
<tr class="level-s" id="level-s">
<th scope="row"><em class="rfc2119">SHOULD</em>‐level error</th>
<td>Non‐conforming, but <em>in some case</em>
conforming.</td>
<td>A violation to a requirement of the specification.
The violation might be legitimize in some case.  Otherwise,
the document is non‐conforming.</td>
</tr>
<tr class="level-w" id="level-w">
<th scope="row">Warning</th>
<td>Conforming.</td>
<td>A warning is an advice from the conformance checker to avoid
to solve a problem in a confusing or possibly wrong way.
It does not affect to the conformance of the document, and
may sometimes be inappropriate.</td>
</tr>
<tr class="level-unsupported" id="level-unsupported">
<th scope="row">Not supported</th>
<td><em>Unknown</em>.</td>
<td>Some feature that is not supported by the conformance checker
is used in the document.</td>
</tr>
</tbody>
</table>
</section>

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

<p>Copyright <time>2007</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>

<!-- $Date: 2007/11/05 09:33:52 $ -->
</body>
</html>