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1  <!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">  <!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">
2  <head>  <head>
3  <title xml:lang="en">Description of Errors —  <base href="cc/">
4  Web Document Conformance Checker (BETA)</title>  
5  <link href="cc-style" rel="stylesheet">  
6    <link href="../cc-style" rel="stylesheet">
7  <link href="#license" rel="license">  <link href="#license" rel="license">
8  </head>  <title xml:lang="en">Description of Errors — WebHACC (β)</title></head>
9  <body>  <body>
10  <h1>Description of Errors</h1>  <header>
11    <h1><a href="../cc-about"><abbr title="Web Hypertext Application Conformance Checker (β)"><img alt="WebHACC" src="../icons/title"></abbr></a></h1>
12    <h2>Description of Errors</h2>
13    </header>
14    
15    
16    
17    <div class="section" id="WebHACC:Heading"><h3>
18        
19      </h3>
20        <p><a href="./#input"><abbr title="Web Hypertext Application Conformance Checker">WebHACC</abbr></a>
21        is a <em>conformance checker</em> (or validator) for Web documents,
22        supporting <a href="../standards">latest Web standards</a> including
23        <a href="http://whatwg.org/html5"><abbr title="Hypertext Markup Language">HTML</abbr>5</a>,
24        <a href="urn:ietf:rfc:4287">Atom 1.0</a>,
25        <a href="http://www.w3.org/Style/CSS/current-work"><abbr title="Cascading Style Sheets">CSS</abbr>3</a>.</p>
26    
27        <p><strong><a href="./#input">Check your document</a></strong>, or
28        <a href="../cc-about">learn more about
29        <abbr title="Web Hypertext Application Conformance Checker">WebHACC</abbr></a>.</p>
30      </div>
31    
32    <section id="character-encoding-layer">
33    <h2>Character Encoding Layer Errors</h2>
34    
35    <div class="section" id="illegal-octets-error"><h3>An illegal octet in the input stream.</h3></div>
36    </section>
37    
38    <section id="html5-character-encoding">
39    <h2>HTML5 Character Encoding Errors</h2>
40    
41    <div class="section" id="disallowed-character-encoding"><h3>Character encoding <code><var>{text}</var></code>
42      is not allowed for <abbr>HTML</abbr> document.</h3>
43        <p>The character encoding used for the document is not allowed
44        for <abbr>HTML</abbr> document.  The document is non‐conforming.</p>
45      </div>
46    
47    <div class="section" id="bad-character-encoding"><h3>Character encoding <code><var>{text}</var></code>
48      should not be used for <abbr>HTML</abbr> document.</h3>
49        <p>The character encoding used for the document is not recommended
50        for <abbr>HTML</abbr> document.  The document is non‐conforming
51        unless there is any good reason to use that encoding.</p>
52      </div>
53    
54    <div class="section" id="non-utf-8-character-encoding"><h3>Use of UTF-8 is encouraged (this document
55      is encoded in <code><var>{text}</var></code>).</h3>
56        <p>Use of UTF-8 as the character encoding of the document is encouraged,
57        though the use of another character encoding is still conforming.</p>
58      </div>
59    
60    <div class="section" id="character-encoding-unchecked"><h3>Conformance for character encoding requirements
61      cannot be checked, since the input is not a byte stream.</h3>
62        <p>The conformance checker cannot detect whether the input document
63        met the requirements on character encoding, since the document
64        is not inputed as a serialized byte sequence.  The document is
65        not conforming if it is not encoded in an appropriate character
66        encoding with appropriate labeling.</p>
67      </div>
68    
69    <div class="section" id="no-character-encoding-declaration"><h3>There is no character encoding
70      declaration.</h3>
71        <p>The document does not contain a character encoding
72        declaration.  Unless the character encoding is explicitly
73        specified in lower‐level protocol, e.g. in <abbr>HTTP</abbr>,
74        or is implied by <abbr>BOM</abbr>, there must be a character
75        encoding declaration.  The document is non‐conforming.</p>
76    
77        <p>The long character encoding declaration syntax
78        <code class="html bad example">&lt;meta http-equiv="Content-Type" content="text/html; charset=<var>charset-name</var>"&gt;</code>
79        is obsolete.  The new syntax is:</p>
80        <pre class="html example">
81    <code>&lt;meta charset="<var>charset-name</var>"&gt;</code></pre>
82    
83        <p>Note that the <code>encoding</code> declaration in <abbr>XML</abbr>
84        declaration has no effect for <abbr>HTML</abbr> document.</p>
85      </div>
86    
87    <div class="section" id="non-ascii-superset"><h3>No character encoding metadata is found
88      in lower‐level protocol nor is there <abbr>BOM</abbr>, while
89      character encoding <code><var>{text}</var></code>
90      is not a superset of <abbr>ASCII</abbr>.</h3>
91        <p>The document is not labeled with character encoding name
92        in lower‐level protocol, e.g. in <abbr>HTTP</abbr>, and
93        the document is not begin with <abbr>BOM</abbr>.  In addition,
94        the character encoding of the document is not a superset of
95        <abbr>ASCII</abbr>.  The document is non‐conforming.</p>
96    
97        <p>Unless there is a <abbr>BOM</abbr>, the character encoding
98        for the document must be specified in e.g. <abbr>HTTP</abbr>‐level,
99        as:</p>
100        <pre class="http example">
101    <code>Content-Type: text/html; charset=<var>charset-name</var></code></pre>
102    
103        <p>Existence of <abbr>HTML</abbr> character encoding declaration, i.e.
104        <code class="html example">&lt;meta charset="<var>charset-name</var>"&gt;</code>,
105        does not allow to omit <code>charset</code> parameter
106        for <abbr>HTML</abbr> document encoded in non‐<abbr>ASCII</abbr>
107        compatible encoding.</p>
108    
109        <p>Character encodings <code>Shift_JIS</code>, <code>Windows-31J</code>,
110        and <code>ISO-2022-JP</code> are <em>not</em> a superset of
111        <abbr>ASCII</abbr> for the purpose of <abbr>HTML</abbr> conformance.</p>
112      </div>
113    
114    <div class="section" id="sniffing:chardet"><h3>Character encoding of this document is sniffed
115      as <code><var>{text}</var></code> (Sniffed because no explicit specification
116      for the character encoding of this document is found in the transfer
117      procotol headers).</h3></div>
118    
119    <div class="section" id="sniffing:default"><h3>Character encoding of this document is defaulted
120      to <code><var>{text}</var></code> because no explicit specification
121      for the character encoding of this document is found in the transfer
122      procotol headers.</h3></div>
123    
124    <div class="section" id="chardecode:fallback"><h3>Since no decoder for the document character
125      encoding is found, decoder for the character encoding
126      <code><var>{text}</var></code> is used.  Checking results might be
127      <em>wrong</em>.</h3></div>
128    
129    <div class="section" id="chardecode:no-error"><h3>Conformance error checking for the character
130      encoding <code><var>{text}</var></code> is not supported.</h3></div>
131    
132    <div class="section" id="charset-label:matching"><h3>Sniffed character encoding
133      <code><var>{text}</var></code> is same as the character encoding specified
134      in the character encoding declaration.  This is <em>not</em> an
135      error.</h3></div>
136    
137    <div class="section" id="charset-label-detected"><h3>While parsing the document as
138      <code><var>{text}</var></code>, a character encoding declaration specifying
139      a different character encoding is found.  The document
140      is reparsed.</h3>
141        <p>While parsing a document in a character encoding,
142        a character encoding declaration which declares the character
143        encoding of the document as another character encoding is found.
144        The occurence of this warning itself does not make the document
145        non‐conforming.  However, the failure of the first attempt to
146        to detect the character encoding might be a result of non‐conformance
147        of the document.</p>
148    
149        <p>The document will be reparsed from the beginning.  Some error
150        or warning might be reported again.</p>
151    
152        <p>These are suggestions to avoid this warning:</p>
153        <ul>
154        <li>Specify <code>charset</code> parameter in the <code>Content-Type</code>
155        field in the <abbr>HTTP</abbr> header, as:
156        <pre class="HTTP example">
157    <code>Content-Type: text/html; charset="<var>charset-name</var>"</code></pre></li>
158        <li>Put the character encoding declaration
159        (<code class="html example">&lt;meta charset="<var>charset-name</var>"&gt;</code>)
160        just after <code class="html example">&lt;head&gt;</code> start tag.</li>
161        <li>Use <code>UTF-8</code>.</li>
162        </ul>
163      </div>
164    
165    <div class="section" id="NULL"><h3>The <code class="charname">NULL</code> character
166      is not allowed.</h3></div>
167    
168    <div class="section" id="control-char"><h3>Code point <code><var>{text}</var></code> is
169      not allowed.</h3></div>
170    
171    </section>
172    
173  <section id="html5-tokenize-error">  <section id="html5-tokenize-error">
174  <h2>HTML5 Parse Errors in Tokenization Stage</h2>  <h2>HTML5 Parse Errors in Tokenization Stage</h2>
175    
176  <div class="section tokenize-error" id="duplicate-attribute"><h3>There are two attributes with same name.</h3>  <div class="section" id="bad-attribute-name"><h3>Attribute name cannot contain characters
177      <p>Attributes must be unique in an element.  Specifying    <code>"</code>, <code>'</code>, and <code>=</code>.</h3></div>
178      attributes with same name more than once is non-conforming.</p>  
179    <div class="section" id="bad-attribute-value"><h3>Attribute value must be quoted by <code>"</code>
180      or <code>'</code> if it contains a <code>"</code>, <code>'</code>, or
181      <code>=</code> character.</h3>
182        <p>In an unquoted attribute value, a character <code>"</code>
183        (<code>U+0022</code> <code class="charname">QUOTATION MARK</code>),
184        <code>'</code> (<code>U+0026</code>
185        <code class="charname">APOSTROPHE</code>), or <code>=</code>
186        (<code>U+003D</code> <code class="charname">EQUAL SIGN</code>)
187        is contained.  These characters are not allowed in unquoted attribute
188        values, since they are used to quote attribute values or to separate
189        attribute name and value.</p>
190    
191        <p>This error is also raised if one try to use empty attribute
192        value like <code class="html bad example">&lt;foo bar= baz=&gt;</code>;
193        in this example, <code class="html bad example">baz=</code> is
194        treated as an invalid attribute value for the attribute
195        <code class="html bad example">bar</code>, not as another attribute.</p>
196      </div>
197    
198    <div class="section" id="bare-ero"><h3>The <code>&amp;</code> character must
199      be escaped as <code class="html example">&amp;amp;</code>.</h3>
200        <p>An <code>&amp;</code> character which
201        is not part of any reference appears in the input stream.
202        The document is non‐conforming.</p>
203    
204        <p><em>Any <code>&amp;</code> character in URI (or IRI)
205        must be escaped as <code class="example">&amp;amp;</code>.</em></p>
206    
207        <p>The <code>&amp;</code> character must
208        be the first character of a reference:
209          <dl class="switch">
210          <dt>Named entity reference</dt>
211              <dd><pre class="html example">
212    <code>&amp;<var>entity-name</var>;</code></pre>
213              where <var>entity-name</var> is the name of the
214              character entity to be referenced.</dd>
215          <dt>Numeric character reference</dt>
216              <dd><pre class="html example">
217    <code>&amp;#<var>d</var>;</code></pre>
218              where <var>d</var> is the decimal representation of
219              the code position of the character to be referenced.</dd>
220          <dt>Hexadecimal character reference</dt>
221              <dd><pre class="html example">
222    <code>&amp;#x<var>h</var>;</code></pre>
223              where <var>h</var> is the hexadecimal representation
224              of the code position of the character to be referenced.</dd>
225          </dl>
226        </p>
227    
228        <p>To represent <code>&amp;</code> as a data character, use
229        named entity reference:
230          <pre class="html example">
231    <code>&amp;amp;</code></pre>
232        </p>
233      </div>
234    
235    <div class="section" id="bare-etago"><h3>A <code>&lt;/</code> string is not followed
236      by a tag name.</h3>
237        <p>There is a <code>&lt;</code> (<code>U+003C</code>
238        <code class="charname">LESS-THAN SIGN</code>) character
239        immediately followed by a <code>/</code> (<code>U+005F</code>
240        <code>SOLIDUS</code>) character, which is not part
241        of any end tag, in the input stream.  The document
242        is non-conforming.</p>
243    
244        <p>The <code>&lt;/</code> sequence immediately followed
245        by an <abbr title="End of file pseudo-character">EOF</abbr> is
246        interpreted as a string data of <code>&lt;/</code>.</p>
247    
248        <p>The <code>&lt;/</code> sequence as string data must
249        be escaped as:
250        <pre class="html example">
251    <code>&amp;lt;/</code></pre>
252        </p>
253      </div>
254    
255    <div class="section" id="bare-stago"><h3>A <code>&lt;</code> character is not followed
256      by tag name or by a <code>!</code> character.</h3>
257        <p>A <code>&lt;</code> (<code>U+003C</code>
258        <code class="charname">LESS-THAN SIGN</code>) character which is not part
259        of any markup appears in the input stream.</p>
260    
261        <p>The <code>&lt;</code> character as a data character must
262        be escaped as:
263        <pre class="html example">
264    <code>&amp;lt;</code></pre>
265        </p>
266      </div>
267    
268    <div class="section" id="bare-nero"><h3>The decimal representation of the code position
269      of a character must be specified after <code>&amp;#</code>.</h3>
270        <p>An <code>&amp;</code> (<code>U+0026</code>
271        <code class="charname">AMPERSAND</code>) character immediately
272        followed by a <code>#</code> (<code>U+0023</code>
273        <code>NUMBER SIGN</code>) character which
274        is not part of any reference appears in the input stream.
275        The document is non-conforming.</p>
276    
277        <p>The string <code>&amp;#</code> must be the first two characters
278        of a reference:
279          <dl class="switch">
280          <dt>Numeric character reference</dt>
281              <dd><pre class="html example">
282    <code>&amp;#<var>d</var>;</code></pre>
283              where <var>d</var> is the decimal representation of
284              the code point of the character to be referenced.</dd>
285          <dt>Hexadecimal character reference</dt>
286              <dd><pre class="html example">
287    <code>&amp;#x<var>h</var>;</code></pre>
288              where <var>h</var> is the hexadecimal representation
289              of the code point of the character to be referenced.</dd>
290          </dl>
291        </p>
292    
293        <p>To represent <code>&amp;#</code> as data characters, use
294        a named entity reference for the <code>&amp;</code> character:
295          <pre class="html example">
296    <code>&amp;amp;#</code></pre>
297        </p>
298      </div>
299    
300    <div class="section" id="bare-hcro"><h3>The hexadecimal representation of the code position
301      of a character must be specified after <code>&amp;#x</code>.</h3>
302       <p>The string <code>&amp;#x</code> or <code>&amp;#X</code> which
303       is not part of any reference appears in the input stream.
304        The document is non-conforming.</p>
305    
306        <p>The string <code>&amp;#x</code> or <code>&amp;#X</code> must
307        be the first three characters of a hexadecimal reference:
308          <pre class="html example">
309    <code>&amp;#x<var>h</var>;</code></pre>
310        where <var>h</var> is the hexadecimal representation
311        of the code point of the character to be referenced.</p>
312    
313        <p>To represent <code>&amp;#x</code> as data characters, use
314        a named entity reference for the <code>&amp;</code> character:
315          <pre class="html example">
316    <code>&amp;amp;#x</code></pre>
317        </p>
318      </div>
319    
320    <div class="section" id="bogus-comment"><h3>String <code>&lt;!</code> is not followed
321      by <code>--</code>.</h3>
322        <p>There is a <code>&lt;</code> (<code>U+003C</code>
323        <code class="charname">LESS-THAN SIGN</code>) character
324        followed by a <code>!</code> (<code>U+0021</code>
325        <code class="charname">EXCLAMATION MARK</code>) character,
326        which is not followed by a <code>--</code> or
327        <code>!DOCTYPE</code>.  The document is non-conforming.</p>
328    
329        <dl class="switch">
330        <dt>Comments</dt>
331          <dd>In HTML document, comments must be introduced by
332          <code class="example">&lt;!--</code> (<code>&lt;!</code>
333          <em>immediately</em> followed
334          by <em>two</em> <code>-</code>s) and must be terminated by
335          <code class="example">--&gt;</code>.
336          Strings <code>&lt;!</code> not followed
337          by <code>--</code> and <code>&lt;!-</code> not followed by
338          <code>-</code> are not valid open delimiters for comments.</dd>
339        <dt>Marked sections, including <code>CDATA</code> sections</dt>
340          <dd>Marked sections are not allowed in HTML document.</dd>
341        <dt>Markup declarations</dt>
342          <dd>Markup declarations, except for <code>DOCTYPE</code>
343          and comment declarations, are not allowed in HTML document.</dd>
344        <dt>String <code>&lt;!</code></dt>
345          <dd>String <code>&lt;!</code> must be escaped as
346          <code class="example">&amp;lt;!</code>.</dd>
347        </dl>
348      </div>
349    
350    <div class="section" id="bogus-end-tag"><h3>String <code>&lt;/</code> is not followed
351      by tag name.</h3>
352        <p>There is a <code>&lt;</code> (<code>U+003C</code>
353        <code class="charname">LESS-THAN SIGN</code>) character
354        immediately followed by a <code>/</code> (<code>U+005F</code>
355        <code>SOLIDUS</code>) character, which is not part
356        of any end tag, in the input stream.  The document
357        is non-conforming.</p>
358    
359        <p>The <code>&lt;/</code> sequence not followed by a
360        tag name is parsed as an opening of bogus comment.</p>
361    
362        <p>The <code>&lt;/</code> sequence as string data must
363        be escaped as:
364        <pre class="html example">
365    <code>&amp;lt;/</code></pre>
366        </p>
367      </div>
368    
369    <div class="section" id="C1-character-reference"><h3>Character reference to
370      <code><var>{text}</var></code> is not allowed.</h3></div>
371    
372    <div class="section" id="CR-character-reference"><h3>Character reference to
373      <code>U+000D</code> (<code class="charname">CARRIAGE RETURN</code>)
374      is not allowed.</h3></div>
375    
376    <div class="section" id="dash-in-comment"><h3>There is a <code>--</code> sequence
377      in a comment.</h3>
378        <p>There is a <code>-</code> (<code>U+002D</code>
379        <code class="charname">HYPHEN-MINUS</code>) character
380        at the end of the comment or a <code>--</code> sequence
381        in the comment.  The document is non-conforming.</p>
382    
383        <p>Comments cannot contain a string <code>--</code>, as in XML.
384        Unlike SGML, there cannot be more than one comments
385        (where <i>comment</i> is an SGML term) in the comment
386        declaration.</p>
387      </div>
388    
389    <div class="section" id="duplicate-attribute"><h3>There are two attributes with name
390          <code><var>{text}</var></code>.</h3>
391        <p>There are more than one attributes with the same
392        name in a tag.  The document is non-conforming.</p>
393    
394      <p>The <code>motion</code> attribute is not part of the HTML standard.      <p>The <code>motion</code> attribute is not part of the HTML standard.
395      Use <code>img</code> element with animation GIF instead.</p>      Use <code>img</code> element with animation GIF instead.</p>
396    </div>    </div>
397    
398  <div class="section tokenize-error" id="nestc"><h3>Void element syntax (<code>/&gt;</code>) cannot be  <div class="section" id="empty-start-tag"><h3>Empty start tag (<code>&lt;&gt;</code>) is not
399      allowed.</h3></div>
400    
401    <div class="section" id="empty-end-tag"><h3>Empty end tag (<code>&lt;/&gt;</code>) is not
402      allowed.</h3></div>
403    
404    <div class="section" id="end-tag-attribute"><h3>End tag cannot have attributes.</h3></div>
405    
406    <div class="section" id="empty-unquoted-attribute-value"><h3>Attribute value is not specified.</h3>
407        <p>The attribute value is not specified after the <code>=</code>
408        (<code>U+003C</code> <code class="charname">EQUAL SIGN</code>)
409        character.</p>
410    
411        <p>When an attribute value is empty, the <code>=</code> character after
412        the attribute name must be specified as:</p>
413    
414        <p><code class="html example">&lt;foo bar&gt;</code></p>
415    
416        <p>Instead, quotation marks can be used to explicitly represent that
417        the attribute value is empty, as:</p>
418    
419        <p><code class="html example">&lt;foo bar=""&gt;</code></p>
420    
421        <p>... or like:</p>
422    
423        <p><code class="html example">&lt;foo bar=''&gt;</code></p>
424      </div>
425    
426    <div class="section" id="invalid-character-reference"><h3>Character reference to
427      <code><var>{text}</var></code> is not allowed.</h3></div>
428    
429    <div class="section" id="nestc"><h3>Polytheistic slash (<code>/&gt;</code>) cannot be
430    used for this element.</h3>    used for this element.</h3>
431      <p>The void element syntax <code>/&gt;</code> syntax can only be      <p>Polytheistic slash (<code>/&gt;</code>) must not be used
432        for the element.  The document is non-conforming.</p>
433    
434        <p>The polytheistic slash can only be
435      used for <code>base</code>, <code>link</code>, <code>meta</code>,      used for <code>base</code>, <code>link</code>, <code>meta</code>,
436      <code>hr</code>, <code>br</code>, <code>img</code>,      <code>hr</code>, <code>br</code>, <code>img</code>,
437      <code>embed</code>, <code>param</code>, <code>area</code>,      <code>embed</code>, <code>param</code>, <code>area</code>,
438      <code>col</code>, and <code>input</code> elements.      <code>col</code>, and <code>input</code> elements.</p>
439      For any other elements, using that syntax is non-conforming.</p>  
440        <dl class="switch">
441        <dt><code>&lt;script/&gt;</code></dt>
442            <dd><p>The polytheistic slash cannot be used for <code>script</code>
443            element.  Even for an empty <code>script</code> element,
444            there must be an explicit end tag
445            <code class="html example">&lt;/script&gt;</code>.</p>
446    
447            <p><strong>NOTE</strong>: Though some user agents interpret
448            polytheistic slash for <code>script</code> element as the
449            closing of the element, such usage is not allowed under
450            the current standard.</p></dd>
451        <dt><code>&lt;basefont/&gt;</code>, <code>&lt;bgsound/&gt;</code>,
452        <code>&lt;frame/&gt;</code>, <code>&lt;keygen/&gt;</code>,
453        <code>&lt;spacer/&gt;</code>, <code>&lt;wbr/&gt;</code></dt>
454            <dd>These elements are themselves non-conforming.</dd>
455        <!-- isindex, image -->
456        <dt><code>&lt;command/&gt;</code>, <code>&lt;event-source/&gt;</code>,
457        <code>&lt;nest/&gt;</code>, or <code>&lt;source/&gt;</code></dt>
458            <dd>Future revision of HTML5 parsing algorithm is expected
459            to allow polytheistic slash for these elements.</dd>
460        <dt><code>&lt;a/&gt;</code>, <code>&lt;p/&gt;</code></dt>
461            <dd>These elements are not always empty and therefore
462            polytheistic slash is not allowed.  Use explicit end tag
463            to represent empty element as:
464              <pre class="example html">
465    <code>&lt;p&gt;&lt;/p&gt;</code></pre>
466            </dd>
467        </dl>
468    
469      <p>Unlike XML, the void element syntax (<code>/&gt;</code>) has      <p>Note that, unlike in XML, the polytheistic slash has
470      no effect in HTML.</p>      no effect in HTML.</p>
471    </div>    </div>
472    
473    <div class="section" id="no-DOCTYPE-name"><h3>After the string <code>&lt;!DOCTYPE </code>, the
474      document type name must be specified.</h3></div>
475    
476    <div class="section" id="no-PUBLIC-literal"><h3>After the keyword <code>PUBLIC</code>, no
477      oublic identifier is specified.</h3></div>
478    
479    <div class="section" id="no-refc"><h3>Character reference must be closed by a
480      <code>;</code> character.</h3></div>
481    
482    <div class="section" id="no-space-before-DOCTYPE-name"><h3>After the string <code>&lt;!DOCTYPE</code>, there
483      must be at least a white space character before the document type
484      name.</h3></div>
485    
486    <div class="section" id="no-space-between-attributes"><h3>Attributes must be separeted by at least a
487      white space character.</h3></div>
488    
489    <div class="section" id="no-SYSTEM-literal"><h3>After the keyword <code>SYSTEM</code>, no
490      system identifier is specified.</h3></div>
491    
492    <div class="section" id="pio"><h3>Processing instruction
493      (<code>&lt;?<var>...</var>&gt;</code>) is not allowed in HTML
494      document.</h3>
495        <p>Processing instructions (<code>&lt;?<var>...</var>?&gt;</code>),
496        including XML declaration (<code>&lt;?xml <var>...</var>?&gt;</code>)
497        and XML style sheet <abbr title="processing instruction">PI</abbr>
498        (<code>&lt;?xml-stylesheet <var>...</var>?&gt;</code>), are not allowed
499        in the HTML syntax.  The document is non-conforming.</p>
500    
501        <dl class="switch">
502        <dt><code>&lt;?xbl?&gt;</code> (<abbr>XBL</abbr> Association)</dt>
503          <dd>An <abbr>XBL</abbr> binding cannot be associated by
504          <abbr title="processing instruction">PI</abbr> in <abbr>HTML</abbr>
505          document.  Use <code>binding</code> property in <abbr>CSS</abbr>
506          style sheet as:
507            <pre class="html example">
508    <code>&lt;style&gt;
509    p {
510      binding: url(binding.xbl);
511    }
512    &lt;/style&gt;</code></pre>
513          </dd>
514        <dt><code>&lt;?xml?&gt;</code> (XML declaration)</dt>
515            <dd>XML declaration is unnecessary for HTML documents.</dd>
516        <dt><code>&lt;?xml-stylesheet?&gt;</code> (XML style sheet
517        <abbr title="processing instruction">PI</abbr>)</dt>
518            <dd>Use HTML <code>link</code> element with <code>rel</code>
519            attribute set to <code>stylesheet</code> (or,
520            <code>alternate stylesheet</code> for an alternate style
521            sheet).
522              <pre class="example html">
523    <code>&lt;link rel=stylesheet href="path/to/stylesheet.css"&gt;</code></pre>
524            </dd>
525        <dt><code>&lt;?php?&gt;</code> or
526        <code>&lt;? <var>... <abbr>PHP</abbr> code ...</var> ?&gt;</code>
527        (<abbr>PHP</abbr> code)</dt>
528            <dd>The conformance checker does <em>not</em> support
529            checking for PHP source documents.</dd>
530        <dt>Other processing instructions</dt>
531            <dd>Processing instructions cannot be inserted in an HTML
532            document.  Use XML document or insert
533            <code>ProcessingInstruction</code> node by scripting.</dd>
534        </dl>
535    
536        <p>Web browsers will parse processing instructions as bogus
537        comments.  Some legacy Web browsers, such as IE:mac and
538        some mobile Web browsers, will display processing instructions
539        as string.</p>
540      </div>
541    
542    <div class="section" id="string-after-DOCTYPE-name"><h3>There is a bogus string after the document type
543      name.</h3></div>
544    
545    <div class="section" id="string-after-PUBLIC"><h3>There is a bogus string after the keyword
546      <code>PUBLIC</code>.</h3></div>
547    
548    <div class="section" id="string-after-PUBLIC-literal"><h3>There is a bogus string after the public
549      identifier.</h3></div>
550    
551    <div class="section" id="string-after-SYSTEM"><h3>There is a bogus string after the keyword
552      <code>SYSTEM</code>.</h3></div>
553    
554    <div class="section" id="string-after-SYSTEM-literal"><h3>There is a bogus string after the system
555      identifier.</h3></div>
556    
557    <div class="section" id="unclosed-attribute-value"><h3>Attribute value is not closed by a quotation
558      mark.</h3></div>
559    
560    <div class="section" id="unclosed-comment"><h3>Comment is not closed by a string
561      <code>--&gt;</code>.</h3></div>
562    
563    <div class="section" id="unclosed-DOCTYPE"><h3>The <code>DOCTYPE</code> is not closed by a
564      <code>&gt;</code> character.</h3></div>
565    
566    <div class="section" id="unclosed-PUBLIC-literal"><h3>The public identifier literal is not closed by a
567      quotation mark.</h3></div>
568    
569    <div class="section" id="unclosed-SYSTEM-literal"><h3>The system identifier literal is not closed by a
570      quotation mark.</h3></div>
571    
572    <div class="section" id="unclosed-tag"><h3>Tag is not closed by a <code>&gt;</code>
573      character.</h3></div>
574    
575  </section>  </section>
576    
577  <section id="html5-parse-errors">  <section id="html5-parse-errors">
578  <h2>HTML5 Parse Errors in Tree Construction Stage</h2>  <h2>HTML5 Parse Errors in Tree Construction Stage</h2>
579    
580  <div class="section parse-error" id="after-head"><h3>The <code><var>$0</var></code> element cannot be  <div class="section" id="after-body"><h3>Start tag <code>&lt;<var>{text}</var>&gt;</code> is
581    inserted between <code>head</code> and <code>body</code> elements.</h3>    not allowed after the <code>body</code> is closed.</h3></div>
582      <p>A start tag occurs after the <code>head</code> element is closed  
583    <div class="section" id="after-body:/"><h3>End tag <code>&lt;/<var>{text}</var>&gt;</code> is
584      not allowed after the <code>body</code> is closed.</h3></div>
585    
586    <div class="section" id="after-body:#text"><h3>Non‐white‐space characters are not allowed
587      after the <code>body</code> is closed.</h3></div>
588    
589    <div class="section" id="after-frameset"><h3>Start tag <code>&lt;<var>{text}</var>&gt;</code> is
590      not allowed after the <code>frameset</code> is closed.</h3></div>
591    
592    <div class="section" id="after-frameset:/"><h3>End tag <code>&lt;/<var>{text}</var>&gt;</code> is
593      not allowed after the <code>frameset</code> is closed.</h3></div>
594    
595    <div class="section" id="after-frameset:#text"><h3>Non‐white‐space characters are not allowed
596      after the <code>frame</code> is closed.</h3></div>
597    
598    <div class="section" id="after-head"><h3>The <code><var>{text}</var></code> element cannot be
599      inserted between <code>head</code> and <code>body</code>
600      elements.</h3>
601        <p>A start tag appears after the <code>head</code> element is closed
602      but before the <code>body</code> element is opened.      but before the <code>body</code> element is opened.
603      The document is non-conforming.</p>      The document is non-conforming.</p>
604    </div>    </div>
605    
606  <div class="section parse-error" id="no-DOCTYPE"><h3>This document does not start with the  <div class="section" id="after-html"><h3>Start tag <code>&lt;<var>{text}</var>&gt;</code> is
607    <code>DOCTYPE</code> declaration.</h3></div>    not allowed after the <code>html</code> is closed.</h3>
608        <p>The start tag of an element appears after the
609        <code>body</code> element has been closed.  The document is
610        non-conforming.</p>
611    
612        <p>Any content of the document other than <code>head</code>
613        contents and comments must be put into the <code>body</code>
614        element.</p>
615      </div>
616    
617    <div class="section" id="after-html:/"><h3>End tag <code>&lt;/<var>{text}</var>&gt;</code> is
618      not allowed after the <code>html</code> is closed.</h3>
619        <p>The end tag of an element appears after the
620        <code>body</code> element has been closed.  The document is
621        non-conforming.</p>
622    
623        <p>Any content of the document other than <code>head</code>
624        contents and comments must be put into the <code>body</code>
625        element.</p>
626      </div>
627    
628    <div class="section" id="after-html:#text"><h3>Non‐white‐space characters are not allowed
629      after the <code>html</code> is closed.</h3></div>
630    
631    <div class="section" id="image"><h3>The <code>image</code> element is
632      obsolete.</h3></div>
633    
634    <div class="section" id="in-a:a"><h3>Anchor cannot be nested.</h3>
635        <p>HTML <code>a</code> elements cannot be nested.
636        The document is non-conforming.</p>
637    
638        <p>In the HTML syntax, a start tag of the <code>a</code>
639        implies the end tag of any opening <code>a</code> element.</p>
640      </div>
641    
642    <div class="section" id="in-body"><h3>Start tag <code>&lt;<var>{text}</var>&gt;</code>
643      is not allowed in the <code>body</code> element.</h3>
644        <p>The start or end tag of an element, which
645        cannot be a descendant of <code>body</code> element, appears
646        in the input stream while the <code>body</code> element has been opened.
647        The document is non-conforming.</p>
648      </div>
649    
650    <div class="section" id="in-body:#eof"><h3>Some element is not closed before the end of
651      file.</h3></div>
652    
653    <div class="section" id="in-button:button"><h3>The <code>button</code> element cannot be
654      nested.</h3></div>
655    
656    <div class="section" id="in-CDATA:#eof"><h3>Element is not closed before the end of
657      file.</h3></div>
658    
659    <div class="section" id="in-form:form"><h3>Start tag <code>&lt;form&gt;</code> is
660      not allowed in a <code>form</code> element.</h3></div>
661    
662    <div class="section" id="in-frameset"><h3>Start tag <code>&lt;<var>{text}</var>&gt;</code> is
663      not allowed in a <code>framset</code> element.</h3></div>
664    
665    <div class="section" id="in-frameset:/"><h3>End tag <code>&lt;/<var>{text}</var>&gt;</code> is
666      not allowed in a <code>frameset</code> element.</h3></div>
667    
668    <div class="section" id="in-frameset:#text"><h3>Non‐white‐space characters are not allowed
669      in a <code>frameset</code> element.</h3></div>
670    
671    <div class="section" id="in-head:head"><h3>Start tag <code>&lt;head&gt;</code>
672      is not allowed in the <code>head</code> element.</h3>
673        <p>There is a start tag <code>&lt;head&gt;</code> in the
674        <code>&lt;head&gt;</code> element.  The document is non-conforming.</p>
675    
676        <p>In an HTML document there must not be more than
677        one <code>head</code> element, therefore no more than one
678        start tag <code>&lt;head&gt;</code> can appear in the input stream.</p>
679      </div>
680    
681    <div class="section" id="in-html:#DOCTYPE"><h3>A <code>DOCTYPE</code> appears after any
682      element or data character has been seen.</h3>
683        <p>A <code>DOCTYPE</code> appears after any element or data character
684        has been seen.  The document is non-conforming.</p>
685        
686        <p>The <code>DOCTYPE</code> must be placed before any
687        tag, reference, or data character.  Only white space characters
688        and comments can be inserted before the <code>DOCTYPE</code>.</p>
689      </div>
690    
691    <div class="section" id="in-nobr:nobr"><h3>The <code>nobr</code> element cannot be
692      nested.</h3></div>
693    
694    <div class="section" id="in-noscript"><h3>The <code><var>{text}</var></code> element is not
695      allowed in a <code>noscript</code> element in the
696      <code>head</code> element.</h3></div>
697    
698    <div class="section" id="in-noscript:/"><h3>An end tag <code>&lt;/<var>{text}</var>&gt;</code>
699      appers before the <code>noscript</code> element is closed.</h3></div>
700    
701    <div class="section" id="in-noscript:#eof"><h3>A <code>noscript</code> element is not closed
702      before the end of file.</h3></div>
703    
704    <div class="section" id="in-noscript:#text"><h3>Non‐white‐space characters are not allowed
705      in a <code>noscript</code> element in the <code>head</code>
706      element.</h3></div>
707    
708    <div class="section" id="in-PCDATA:#eof"><h3>Element is not closed before the end of
709      file.</h3></div>
710    
711    <div class="section" id="in-select"><h3>Start tag <code>&lt;<var>{text}</var>&gt;</code>
712      is not allowed in a <code>select</code> element.</h3></div>
713    
714    <div class="section" id="in-select:/"><h3>End tag <code>&lt;/<var>{text}</var>&gt;</code>
715      is not allowed in a <code>select</code> element.</h3></div>
716    
717    <div class="section" id="in-table"><h3>Start tag <code>&lt;<var>{text}</var>&gt;</code>
718      is not allowed in a <code>table</code> element.</h3>
719        <p>The start or end tag of an element, which
720        cannot be a child of <code>table</code> element, appears
721        in the input stream while the <code>table</code> element has been opened
722        but no other element has been opened.  The document is non-conforming.</p>
723    
724        <p>In <code>table</code>, only table related elements
725        are allowed; any other element must be contained in
726        <code>td</code> or <code>th</code> element to form
727        a part of the table, or <code>caption</code> element to create
728        a table caption.</p>
729      </div>
730    
731    <div class="section" id="in-table:/"><h3>End tag <code>&lt;/<var>{text}</var>&gt;</code>
732      is not allowed in a <code>table</code> element.</h3></div>
733    
734    <div class="section" id="in-table:#text"><h3>Non‐white‐space character is not allowed within
735      the <code>table</code> element, outside of the caption and cells.</h3>
736        <p>A non‐white‐space character appears in <code>table</code>.
737        The document is non-conforming.</p>
738    
739        <p>In <code>table</code>, only table related elements
740        are allowed; any other element and data character must be contained in
741        <code>td</code> or <code>th</code> element to form
742        a part of the table, or <code>caption</code> element to create
743        a table caption.</p>
744      </div>
745    
746    <div class="section" id="isindex"><h3>The <code>isindex</code> element is
747      obsolete.</h3></div>
748    
749    <div class="section" id="missing-start-tag:tr"><h3>Start tag of <code>tr</code>
750      element is missing.</h3>
751        <p>Start tag of a <code>tr</code> element, which is <em>not</em>
752        optional, is missing.  The document is non-conforming.</p>
753    
754        <p>In a table section, a <code>&lt;tr&gt;</code> start tag
755        must occur before any <code>&lt;td&gt;</code> or
756        <code>&lt;th&gt;</code> start tag.  Though the HTML5 parser
757        implies the <code>&lt;tr&gt;</code> start tag before
758        these start tags, it must be explicitly specified.</p>
759      </div>
760    
761    <div class="section" id="no-DOCTYPE"><h3>This document does not start with a
762      <code>DOCTYPE</code>.</h3>
763        <p>The document does not start with a <code>DOCTYPE</code>.
764        The document is non-conforming.</p>
765    
766        <p>An HTML document must start by a <code>DOCTYPE</code>:
767          <pre class="html example">
768    <code>&lt;!DOCTYPE HTML&gt;</code></pre>
769        </p>
770    
771        <p>Only white space characters and comments are allowed
772        before the <code>DOCTYPE</code>.  XML declaration is <em>not</em>
773        allowed in HTML document.</p>
774      </div>
775    
776    <div class="section" id="not-closed"><h3>Element <code><var>{text}</var></code> is not
777      closed.</h3>
778        <p>End tag of an element is not found before, for example,
779        an end tag of another element appears or
780        the end of the document.  The document is non-conforming.</p>
781    
782        <p>Only <code>body</code>, <code>colgroup</code>, <code>dd</code>,
783        <code>dt</code>, <code>head</code>, <code>html</code>, <code>li</code>,
784        <code>ol</code>, <code>option</code>, <code>optgroup</code>,
785        <code>p</code>, <code>rb</code>, <code>rp</code>, <code>rt</code>,
786        <code>tbody</code>, <code>td</code>, <code>tfoot</code>,
787        <code>th</code>, <code>thead</code>, <code>tr</code>,
788        <code>ul</code> end tag can be omitted in HTML documents.
789        For any element except for void element, there must be an explicit
790        end tag.</p>
791    
792        <dl class="switch">
793        <dt>HTML <code>canvas</code> element</dt>
794          <dd>Though the element is void in earlier versions of Safari,
795          the <code>canvas</code> element is <em>no</em> longer
796          defined as empty.  There must be an end tag
797          <code class="html example">&lt;/canvas&gt;</code>.</dd>
798        </dl>
799    
800        <p>Note that misnesting tags, such as
801        <code class="bad example">&lt;a&gt;&lt;b&gt;&lt;/a&gt;&lt;/b&gt;</code>, are not
802        allowed and they also cause this error.</p>
803      </div>
804    
805  <div class="section parse-error" id="not-closed"><h3>Element <code><var>$0</var></code> is not  <div class="section" id="not-first-start-tag"><h3>This <code>&lt;html&gt;</code> tag is not
806    closed.</h3></div>    the first start tag.</h3>
807        <p>There is a start tag of the <code>html</code> element
808        that it not the first start tag in the input stream.
809        The document is non-conforming.</p>
810    
811  <div class="section parse-error" id="not-HTML5"><h3>This document is written in an old version of      <p>In an HTML document, there cannot be more than one
812    HTML.</h3></div>      <code>html</code> element and therefore there cannot be
813        more than one <code>&lt;html&gt;</code> tag.  In addition,
814        nothing can be placed before the <code>&lt;html&gt;</code> tag
815        except a <code>DOCTYPE</code>, white space characters,
816        and comments.</p>
817      </div>
818    
819  <div class="section parse-error" id="unmatched-end-tag"><h3>Element <code><var>$0</var></code> is not  <div class="section" id="not-HTML5"><h3>This document is written in an old version of
820    opened.</h3></div>    HTML.</h3>
821        <p>The document contains a <code>DOCTYPE</code> declaration
822        that is different from HTML5 <code>DOCTYPE</code> (i.e.
823        <code class="example html">&lt;!DOCTYPE HTML&gt;</code>).
824        The document is non‐conforming.</p>
825    
826        <p>The document might or might not be conformant to
827        some version of HTML.  However, conformance to any HTML
828        specification other than HTML5 provides for no practical
829        convenience, since Web borwsers will parse any
830        HTML document (roughly) as defined in HTML5.</p>
831      </div>
832    
833    <div class="section" id="start-tag-not-allowed"><h3>Start tag <code>&lt;<var>{text}</var>&gt;</code> is
834      not allowed here.</h3></div>
835    
836    <div class="section" id="unmatched-end-tag"><h3>Element <code><var>{text}</var></code> is not
837      opened.</h3>
838        <p>An end tag appears though no element with the same name
839        has been opened.  The document is non-conforming.</p>
840    
841        <p>For any end tag in HTML document, there must be a
842        corresponding start tag.</p>
843    
844        <dl class="switch">
845        <dt>HTML <code>base</code>, <code>basefont</code>,
846        <code>bgsound</code>, <code>br</code>, <code>col</code>,
847        <code>embed</code>, <code>frame</code>, <code>hr</code>,
848        <code>image</code>, <code>img</code>, <code>input</code>,
849        <code>isindex</code>, <code>link</code>, <code>meta</code>,
850        <code>param</code>, <code>spacer</code>, or <code>wbr</code> element</dt>
851          <dd>End tag is not allowed for these elements, since
852          those content must always be empty.  Remove end tag.</dd>
853        <!-- keygen -->
854        <!-- command, event-source, nest, source -->
855        </dl>
856      </div>
857    
858  </section>  </section>
859    
860  <section id="element-content-model-errors">  <section id="element-content-model-errors">
861  <h2>Element Content Model Errors</h2>  <h2>Element Content Model Errors</h2>
862    
863  <div class="section content-model-error" id="character-not-allowed"><h3>Data character is not allowed in this  <div class="section" id="basehref-after-URL-attribute"><h3>The <code>base</code> element with the
864      <code>href</code> attribute specified cannot be placed after
865      any attribute with a URL.</h3></div>
866    
867    <div class="section" id="basetarget-after-hyperlink"><h3>The <code>base</code> element with the
868      <code>target</code> attribute specified cannot be placed after
869      any element that defines a hyperlink.</h3></div>
870    
871    <div class="section" id="character-not-allowed"><h3>Data character is not allowed in this
872    context.</h3>    context.</h3>
873      <p>A data character occurs where it is not allowed in this      <p>A data character appears where it is not allowed in this
874      context.  The document is non-conforming.</p>      context.  The document is non-conforming.</p>
875    
876      <p>Possible causes:      <p>Possible causes:
877        <dl>        <ul>
878        <dt>If the erred element is an inline-level element (such        <li><p>A data character cannot be a child
879        as <code>a</code> or <code>span</code>)</dt>        of certain sectioning elements such as <code>body</code>,
880            <dd><p>A data character cannot be a child        <code>section</code>, and <code>blockquote</code>.</p>
881            of certain sectioning elements such as <code>body</code>,  
882            <code>section</code>, and <code>blockquote</code>.</p>        <p>Any inline-level content must be put
883          in e.g. paragraph element such as <code>p</code>.</p></li>
884            <p>Any inline-level content must be put        <li><p>Though some elements such as <code>div</code>,
885            in e.g. paragraph element such as <code>p</code>.</p></dd>        <code>li</code>, and <code>td</code> allow
886        <dt>If the erred element is a block-level element (such as        <em>either one</em> of block-level or inline-level content
887        <code>div</code> or <code>h<var>n</var></code>)</dt>        is allowed.  If there is a block-level content,
888            <dd><p>Though some elements such as <code>div</code>,        any inline-level content must be put
889            <code>li</code>, and <code>td</code> allow        in e.g. paragraph element such as <code>p</code>.</p></li>
890            <em>either one</em> of block-level or inline-level content        </ul>
           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></dd>  
       </dl>  
891      </p>      </p>
892    </div>    </div>
893    
894  <div class="section content-model-error" id="child-element-missing"><h3>There must be a <code><var>$0</var></code>  <div class="section" id="character-not-allowed:empty"><h3>Non‐white‐space characters are not allowed in
895    element as a child of this element.</h3>    an empty element.</h3></div>
896    
897    <div class="section" id="character-not-allowed:atom|PersonConstruct"><h3>Non‐white‐space characters are not allowed in
898      Person construct.</h3></div>
899    
900    <div class="section" id="character-not-allowed:atom|TextConstruct"><h3>Non‐white‐space characters are not allowed in
901      Text construct.</h3></div>
902    
903    <div class="section" id="child-element-missing"><h3>There must be an element
904      <code><var>{text}</var></code> as a child of this element.</h3>
905      <p>The content model of the element is so defined that it      <p>The content model of the element is so defined that it
906      must contain a <code><var>$0</var></code> child element.      must contain a <code><var>$0</var></code> child element.
907      Without such an element, the document is non-conforming.</p>      The document is non-conforming.</p>
908    
909      <p>For example:      <dl class="switch">
910        <ul>      <dt>HTML <code>head</code> element</dt>
911        <li>The <code>head</code> element must contain exactly one        <dd>There must be a <code>title</code> child element.</dd>
912        <code>title</code> child element.</li>      <dt>HTML <code>html</code> element</dt>
913        <li><a href="#child-element-missing:td%7Cth">The <code>tr</code>        <dd>There must be a <code>head</code> child element followed
914        element must contain one or more <code>td</code> or <code>th</code>        by a <code>body</code> element.</dd>
915        child element.</a></li>      <dt>HTML <code>tr</code> element</dt>
916        </ul>        <dd><a href="#child-element-missing:td%7Cth">There must be
917      </p>        one or more <code>td</code> or <code>th</code> child element.</a></dd>
918        </dl>
919    </div>    </div>
920    
921  <div class="section content-model-error" id="child-element-missing:td|th"><h3>There must be a <code>td</code>  <div class="section" id="child-element-missing:td|th"><h3>There must be a <code>td</code>
922    or <code>th</code> element as a child of this element.</h3>    or <code>th</code> element as a child of this element.</h3>
923      <p>The <code>tr</code> element must contain at least one      <p>The <code>tr</code> element must contain at least one
924      <code>td</code> or <code>th</code> child element.  Without      <code>td</code> or <code>th</code> child element.  The document
925      such an element, the document is non-conforming.</p>      is non-conforming.</p>
926    </div>    </div>
927    
928  <div class="section content-model-error" id="element-not-allowed"><h3>This element is not allowed in this  <div class="section" id="child-element-missing:atom"><h3>There must be an element
929      <code><var>{text}</var></code> in the Atom namespace as a child of this
930      element.</h3></div>
931    
932    <div class="section" id="child-element-missing:atom:link:alternate"><h3>There must be an Atom <code>link</code> element
933      whose <code>rel</code> attribute is set to <code>alternate</code> as a
934      child of this element.</h3></div>
935    
936    <div class="section" id="child-element-missing:atom:link:self"><h3>There should be an Atom <code>link</code> element
937      whose <code>rel</code> attribute is set to <code>self</code> as a
938      child of this element.</h3></div>
939    
940    <div class="section" id="element-missing:hn"><h3>There must be at least one
941      <code>h<var>n</var></code> element descendant.</h3></div>
942    
943    <div class="section" id="element-not-allowed"><h3>This element is not allowed in this
944    context.</h3>    context.</h3>
945      <p>An element occurs where it is not allowed.  The document      <p>An element appears where it is not allowed.  The document
946      is non-conforming.</p>      is non-conforming.</p>
947    
948      <p>Possible causes:      <p>Possible causes:
949        <dl>        <dl class="switch">
950        <dt>If the erred element is an inline-level element (such        <dt>If the element with the error is an inline-level element,
951        as <code>a</code> or <code>span</code>)</dt>        such as <code>a</code>, <code>progress</code>, or <code>img</code></dt>
952            <dd><p>An inline-level element cannot be a child            <dd><p>An inline-level element cannot be a child
953            of certain sectioning elements such as <code>body</code>,            of certain sectioning elements such as <code>body</code>,
954            <code>section</code>, and <code>blockquote</code>.</p>            <code>section</code>, and <code>blockquote</code>.</p>
955    
956            <p>Any inline-level content must be put            <p>Any inline-level content must be put
957            in e.g. paragraph element such as <code>p</code>.</p></dd>            in e.g. paragraph element such as <code>p</code>.</p></dd>
958        <dt>If the erred element is a block-level element (such as        <dt>If it is a block-level elements, such as <code>aside</code>,
959        <code>div</code> or <code>h<var>n</var></code>)</dt>        <code>div</code>, <code>h<var>n</var></code>,
960            <dd><p>Though some elements such as <code>div</code>,        <code>p</code>, or <code>section</code></dt>
961            <code>li</code>, and <code>td</code> allow            <dd><dl class="switch">
962            <em>either one</em> of block-level or inline-level content                <dt>If the parent element is <code>div</code>,
963            is allowed.  If there is a block-level content,                <code>li</code>, <code>td</code>, or <code>th</code></dt>
964            any inline-level content must be put                <!-- @@ TODO: more... -->
965            in e.g. paragraph element such as <code>p</code>.</p></dd>                    <!-- @@ TODO: <p><ul><li><p> -->
966        <dt>If the erred element is the root <code>html</code> element</dt>                    <dd><p>The parent element allows <em>either</em>
967            <dd><p>In an XHTML document, the root <code>html</code>                    block-level or inline-level content.  If there is a
968            element must have an <code>xmlns</code> attribute                    block-level content, any inline-level content must be
969            whose value is set to                    put in e.g. paragraph element such as <code>p</code>.</p>
970            <code>http://www.w3.org/1999/xhtml</code>.</p></dd>                    <p>For example, an HTML document fragment
971                      <code class="html bad example">&lt;div&gt;&lt;p&gt;Hello!&lt;/p&gt; World!&lt;/div&gt;</code>
972                      is non-conforming, since a word <q>World!</q> does not belong
973                      to any paragraph.  (If not part of any paragraph, what is
974                      it!?)  A conforming example would be:
975                        <pre class="html example">
976    <code>&lt;div&gt;&lt;p&gt;Hello!&lt;/p&gt; &lt;p&gt;World!&lt;/p&gt;&lt;/div&gt;</code></pre>
977                      </p></dd>
978                  <dt>If the parent element does <em>not</em> allow
979                  block-level elements as content</dt>
980                      <dd>The element is not allowed to be inserted here.
981                      For example, a <code>div</code> element cannot be
982                      a child of an <code>h1</code> element.</dd>
983              </dl></dd>
984          <dt>If the element with the error is a <code>noscript</code> element</dt>
985              <dd>The <code>noscript</code> element is allowed only in the context
986              where a block-level or inline-level content is expected
987              and in the <code>head</code> element.
988              It cannot be used in e.g. <code>ul</code>, <code>table</code>,
989              or <code>select</code>.</dd>
990          <dt>If the element with the error is <code>blink</code>,
991          <code>center</code>, or <code>marquee</code> element</dt>
992              <dd>These elements are not part of the HTML standard.
993              Use CSS for styling control.</dd>
994    
995          <dt><code>button</code>, <code>datalist</code>,
996          <code>fieldset</code>, <code>form</code>,
997          <code>input</code>, <code>label</code>,
998          <code>optgroup</code>, <code>option</code>, <code>output</code>,
999          <code>rb</code>, <code>rp</code>, <code>rt</code>, <code>ruby</code>,
1000          <code>textarea</code>, or <code>textarea</code> element</dt>
1001          <!-- rbc, rtc ? -->
1002              <dd>These elements are intentionally not supported by the conformance
1003              checker <em>yet</em>.</dd>
1004        </dl>        </dl>
1005      </p>      </p>
1006    </div>    </div>
1007    
1008    <div class="section" id="element-not-allowed:area"><h3>An <code>area</code> element cannot be used
1009      outside of a <code>map</code> element.</h3></div>
1010    
1011    <div class="section" id="element-not-allowed:base"><h3>There is another <code>base</code>
1012      element.</h3></div>
1013    
1014    <div class="section" id="element-not-allowed:datatemplate"><h3>In a <code>datatemplate</code> element, only
1015      <code>rule</code> elements are allowed.</h3></div>
1016    
1017    <div class="section" id="element-not-allowed:details-legend"><h3>In a <code>details</code> element, only at the
1018      beginning of the element a <code>lengend</code> element
1019      may be used.</h3></div>
1020    
1021    <div class="section" id="element-not-allowed:empty"><h3>Elements are not allowed in an empty
1022      element.</h3></div>
1023    
1024    <div class="section" id="element-not-allowed:figure-legend"><h3>In a <code>figure</code> element, only at the
1025      beginning or only at the end of the element a <code>lengend</code> element
1026      may be used.</h3></div>
1027    
1028    <div class="section" id="element-not-allowed:flow"><h3>This element is not allowed where flow
1029      content is expected.</h3></div>
1030    
1031    <div class="section" id="element-not-allowed:flow-style"><h3>A <code>style</code> element without
1032      <code>scoped</code> attribute is not allowed in this context.</h3></div>
1033    
1034    <div class="section" id="element-not-allowed:head-noscript"><h3>This element is not allowed in a
1035      <code>noscript</code> element in the <code>head</code> element.</h3></div>
1036    
1037    <div class="section" id="element-not-allowed:head-style"><h3>A <code>style</code> element with
1038      <code>scoped</code> attribute is not allowed in the <code>head</code>
1039      element.</h3></div>
1040    
1041    <div class="section" id="element-not-allowed:head-title"><h3>There is another <code>title</code>
1042      element.</h3></div>
1043    
1044    <div class="section" id="element-not-allowed:minus"><h3>This element is not allowed in this
1045      context.</h3></div>
1046    
1047    <div class="section" id="element-not-allowed:meta-charset"><h3>The character encoding declaration must be the
1048      first element in the <code>head</code> element.</h3></div>
1049    
1050    <div class="section" id="element-not-allowed:metadata"><h3>This element is not allowed where metadata
1051      content is expected.</h3></div>
1052    
1053    <div class="section" id="element-not-allowed:phrasing"><h3>This element is not allowed where phrasing
1054      content is expected.</h3></div>
1055    
1056    <div class="section" id="element-not-allowed:root"><h3>This element is not allowed as the root
1057      element of a document.</h3>
1058        <p>An element that is not allowed as the root element
1059        is used as the root element of the document.  The document is
1060        non-conforming, as far as the conformance checker can tell.</p>
1061    
1062        <dl class="switch">
1063        <dt><code>html</code> element in an XHTML document</dt>
1064            <dd><p>In <abbr>XHTML</abbr> document, the root <code>html</code>
1065            element must have an <code>xmlns</code> attribute as:
1066              <pre class="xml example">
1067    <code>&lt;html xmlns="http://www.w3.org/1999/xhtml"&gt;</code></pre></p></dd>
1068        <dt><code>rss</code> element</dt>
1069            <dd><p>The document is written in some version of RSS.</p>
1070            <p>The conformance checker does not support any version
1071            of RSS.  Use Atom 1.0 for feed documents.</p></dd>
1072        <dt><code>feed</code> element</dt>
1073            <dd><p>The Atom <code>feed</code> element must be
1074            in the <code>http://www.w3.org/2005/Atom</code>
1075            namespace as:
1076              <pre class="xml example">
1077    <code>&lt;feed xmlns="http://www.w3.org/2005/Atom"&gt;</code></pre>
1078            </p>
1079            <p>The conformance checker does not support Atom 0.3.
1080            Use Atom 1.0 for feed documents.</p></dd>
1081        </dl>
1082      </div>
1083    
1084    <div class="section" id="element-not-allowed:root:xml"><h3>This element is not allowed as the root element
1085      of an XML document.</h3></div>
1086    
1087    <div class="section" id="element-not-allowed:ruby-base"><h3>This element is not allowed in the <code>ruby</code>
1088      element.</h3></div>
1089    
1090    <div class="section" id="element-not-allowed:text"><h3>This element is not allowed in this
1091      context.</h3></div>
1092    
1093    <div class="section" id="element-not-allowed:atom|content"><h3>This element is not allowed in an Atom
1094      <code>content</code> element.</h3></div>
1095    
1096    <div class="section" id="element-not-allowed:atom|PersonConstruct"><h3>This element is not allowed in Person
1097      construct.</h3></div>
1098    
1099    <div class="section" id="element-not-allowed:atom|TextConstruct"><h3>This element is not allowed in Text
1100      construct.</h3></div>
1101    
1102    <div class="section" id="element-not-defined"><h3>This element is not defined.</h3></div>
1103    
1104    <div class="section" id="no-significant-content"><h3>No significant content is contained
1105      in this element.</h3></div>
1106    
1107    <div class="section" id="no-significant-content-before"><h3>There is no significant content
1108      before this element.</h3></div>
1109    
1110    <div class="section" id="no-significant-content-at-the-end"><h3>No significant content is contained
1111      at the end of this element.</h3></div>
1112    
1113    <div class="section" id="ps-element-missing"><h3>There is no <code><var>{text}</var></code>
1114      element before this element.</h3>
1115        <p>There must be an element before another element, but there
1116        is not.  The document is non-conforming.</p>
1117    
1118        <p>For example, there must be a <code>dt</code> element
1119        before any <code>dd</code> element.</p>
1120      </div>
1121    
1122    <div class="section" id="rp:syntax-error"><h3>The content of a <code>rp</code> element must
1123      be a parenthesis.</h3></div>
1124    
1125    </section>
1126    
1127    <section id="attribute-errors">
1128    <h2>Attribute Errors</h2>
1129    
1130    <div class="section" id="attribute-missing"><h3>Required attribute <code><var>{text}</var></code>
1131      is not specified.</h3>
1132        <p>A required attribute is not specified.  The document
1133        is non-conforming.</p>
1134    
1135        <p>Some attribute is defined as <i>required</i>.
1136        Without required attributes specified, user agents
1137        cannot provide full functionality of the element to the user.</p>
1138    
1139        <dl class="switch">
1140        <dt>HTML <code>img</code> element</dt>
1141            <dd>The <code>src</code> attribute must be specified.
1142            Additionally, the <code>alt</code> attribute must be specified
1143            in many cases.</dd>
1144        <dt>HTML <code>link</code> element</dt>
1145            <dd>The <code>rel</code> attribute must be specified.
1146            Note that the <code>rev</code> attribute is obsolete.</dd>
1147        </dl>
1148      </div>
1149    
1150    <div class="section" id="attribute-missing:data|type"><h3>For an <code>object</code> at least one of
1151      <code>data</code> and <code>type</code> attributes must be
1152      specified.</h3></div>
1153    
1154    <div class="section" id="attribute-missing:href|target"><h3>For a <code>base</code> element, at least one of
1155      <code>href</code> and <code>target</code> attributes must be
1156      specified.</h3></div>
1157    
1158    <div class="section" id="attribute-missing:name|http-equiv"><h3>For a <code>meta</code> element with the
1159      <code>content</code> attribute specified, exactly one of
1160      <code>name</code> and <code>http-equiv</code> attributes must be
1161      specified.</h3></div>
1162    
1163    <div class="section" id="attribute-missing:name|http-equiv|charset"><h3>For a <code>meta</code> element, exactly one of
1164      <code>name</code>, <code>http-equiv</code>, and <code>charset</code>
1165      attributes must be specified.</h3></div>
1166    
1167    <div class="section" id="attribute-not-allowed"><h3>Attribute
1168      <code><var>{local-name}</var></code> is not allowed for
1169      <code><var>{element-local-name}</var></code> element.</h3>
1170        <p>An attribute is specified where it is not allowed.
1171        The document is non-conforming.</p>
1172    
1173        <dl>
1174        <dt>HTML <code>meta</code> element</dt>
1175            <dd>For HTML <code>meta</code> element, <em>only one</em> of
1176            <code>name</code>, <code>http-equiv</code>, or <code>charset</code>
1177            attribute is allowed.</dd>
1178        </dl>
1179      </div>
1180    
1181    <div class="section" id="attribute-not-allowed:ismap"><h3>The <code>ismap</code> attribute may only be
1182      used for the image contained in an <code>a</code> element.</h3></div>
1183    
1184    <div class="section" id="attribute-not-defined"><h3>This attribute is not defined.</h3>
1185        <p>The attribute is not one of attributes allowed for the element
1186        in the latest version of relevant specifications.</p>
1187    
1188        <p>The attribute cannot be used.</p>
1189    
1190        <dl>
1191        <dt><code>autosubmit</code> attribute (<code>menu</code> element)</dt>
1192          <dd>The attribute was part of HTML5 draft but then dropped.
1193          Similar functionality can be implemented by scripts.</dd>
1194        </dl>
1195      </div>
1196    
1197    <div class="section" id="in-HTML:xml:lang"><h3>The <code>xml:lang</code> attribute in HTML
1198      document is ignored.</h3>
1199        <p>The <code>xml:lang</code> attribute does not have an effect in
1200        HTML document.</p>
1201    
1202        <p>The <code>xml:lang</code> attribute is only applicable to XML
1203        documents.  In HTML document, it is only allowed to ease migration
1204        from XML.</p>
1205    
1206        <p>To specify natural language information in HTML document,
1207        use <code>lang</code> attribute instead.</p>
1208    
1209        <p>XHTML 1.0 Appendix C was encouraged to specify both
1210        <code>lang</code> and <code>xml:lang</code> attributes with
1211        the same value.  Such a duplication has <em>no effect</em> in practice.
1212        Use only one of <code>lang</code> (in HTML) or <code>xml:lang</code> (in
1213        XML).</p>
1214    
1215        <!-- @@ ISSUE: xml:lang in non-HTML element in DOM5 HTML created
1216             from an HTML document? -->
1217      </div>
1218    
1219    <div class="section" id="in-XML:charset"><h3>The <code>charset</code> attribute is not
1220      allowed in XML document.</h3>
1221        <p>The <code>charset</code> attribute of a
1222        <code>meta</code> element is not allowed in XML document.
1223        The document is non-conforming.</p>
1224    
1225        <p>To specify the character encoding used for serialization,
1226        if necessary, use XML declaration instead:
1227          <pre class="xml example">
1228    <code>&lt;?xml version="1.0" encoding="<var>encoding-name</var>"?&gt;</code></pre>
1229        </p>
1230      </div>
1231    
1232    <div class="section" id="in-XML:noscript"><h3>A <code>noscript</code> element cannot be
1233      used in XML document.</h3></div>
1234    
1235    <div class="section" id="in-XML:xml:lang"><h3>The <code>xml:lang</code> attribute in no namespace
1236      is only allowed in HTML document.</h3></div>
1237    
1238    <div class="section" id="in-XML:xmlns"><h3>The <code>xmlns</code> attribute
1239      in the <code>null</code> namespace is not allowed in
1240      XHTML document.  The document is non-conforming.</h3>
1241        <p>The <code>xmlns</code> attribute in the <code>null</code>
1242        namespace is not allowed in XHTML document.</p>
1243    
1244        <p>This error should not occur in conformance-checking of
1245        static documents.</p>
1246      </div>
1247    
1248    <div class="section" id="xml:lang-not-allowed"><h3>The <code>xml:lang</code> attribute is only allowed
1249      when the <code>lang</code> attribute is specified.</h3></div>
1250    
1251  </section>  </section>
1252    
1253  <section id="attribute-value-errors">  <section id="attribute-value-errors">
1254  <h2>Attribute Value Errors</h2>  <h2>Attribute Value Errors</h2>
1255    
1256  <div class="section attribute-error" id="enumerated:invalid"><h3>This attribute only allow a limited set of  <div class="section" id="boolean:invalid"><h3>Attribute value <code><var>{@}</var></code>
1257    values and the specified value is not one of them.</h3></div>    is not allowed.  It must be an empty string or a string
1258      <code><var>{local-name}</var></code>.</h3></div>
1259    
1260    <div class="section" id="char:syntax-error"><h3>The attribute value must be exactly one
1261      character.</h3></div>
1262    
1263    <div class="section" id="charref-in-charset"><h3>A character reference cannot be used to
1264      represent a character encoding name.</h3></div>
1265    
1266    <div class="section" id="charset:not-preferred"><h3>Character encoding name
1267      <code><var>{value}</var></code> is not the preferred name of that
1268      character encoding.</h3></div>
1269    
1270    <div class="section" id="charset:not-registered"><h3>Character encoding name
1271      <code><var>{value}</var></code> is not a registered name.</h3>
1272        <p>The specified character encoding name is not registered to
1273        <abbr>IANA</abbr>.  Use of registered character encoding name
1274        is a good practice to facilitate interoperability.</p>
1275    
1276        <dl class="switch">
1277        <dt><code>EUC-TW</code></dt>
1278          <dd><code>EUC-TW</code> is not registered.  Unfortunately, there
1279          is no registered name for that character encoding.  Use
1280          Big5 encoding with character encoding name <code>Big5</code>
1281          if it is enough to represent the document.</dd>
1282        <dt><code>ISO-2022-JP-1</code></dt>
1283          <dd><code>ISO-2022-JP-1</code> is not registered, nevertheless
1284          this character encoding name is documented in
1285          <a href="urn:ietf:rfc:2237"><abbr>RFC</abbr> 2237</a>.  Use
1286          <code>ISO-2022-JP-2</code> instead, since that character encoding
1287          is a superset of ISO-2022-JP-1.</dd>
1288        <dt><code>ISO-2022-JP-3</code>, <code>ISO-2022-JP-3-plane1</code></dt>
1289          <dd>These names are not registered and obsoleted in favor of
1290          <code>ISO-2022-JP-2004</code> and
1291          <code>ISO-2022-JP-2004-plane1</code>.</dd>
1292        <dt><code>ISO-2022-JP-2003</code>,
1293        <code>ISO-2022-JP-2003-plane1</code></dt>
1294          <dd>These names are not registered and corrected to
1295          <code>ISO-2022-JP-2004</code> and
1296          <code>ISO-2022-JP-2004-plane1</code>.</dd>
1297        <dt><code>ISO-2022-JP-2004</code>,
1298        <code>ISO-2022-JP-2004-plane1</code></dt>
1299          <dd>These names are not registered.  Unfortunately, there is
1300          no registered name for these character encodings.</dd>
1301        <dt><code>UTF-8N</code></dt>
1302          <dd><code>UTF-8N</code> is not registered.  Character encoding
1303          name <code>UTF-8</code> represents UTF-8 encoding with or
1304          without <abbr>BOM</abbr>.</dd>
1305        </dl>
1306    
1307        <p><strong>WARNING</strong>: This error might be raised for
1308        a registered character encoding name, since the character encoding
1309        name database of the conformance checker is not complete yet.</p>
1310      </div>
1311    
1312    <div class="section" id="charset:private"><h3>Character encoding name
1313      <code><var>{value}</var></code> is a private name.</h3>
1314        <p>The specified character encoding name is a private name and
1315        not registered to <abbr>IANA</abbr>.  Use of registered character
1316        encoding name is a good practice to facilitate interoperability.</p>
1317    
1318        <dl class="switch">
1319        <dt><code>x-euc-jp</code></dt>
1320          <dd>Use <code>EUC-JP</code> for the Japanese <abbr>EUC</abbr>
1321          character encoding.</dd>
1322        <dt><code>x-sjis</code></dt>
1323          <dd>Use <code>Shift_JIS</code> for standard Shift encoding scheme of
1324          <abbr>JIS</abbr> coded character set, or <code>Windows-31J</code>
1325          for Microsoft standard character set as implemented by
1326          Microsoft Windows.</dd>
1327        </dl>
1328      </div>
1329    
1330    <div class="section" id="charset:syntax-error"><h3>The specified value <code><var>{value}</var></code>
1331      is syntactically not a character encoding name.</h3>
1332        <p>The attribute value must be a character encoding name.  However,
1333        the specified value is not a character encoding name syntactically.
1334        The document is non‐conforming.</p>
1335        <p>Character encoding name is a string of <abbr>ASCII</abbr>
1336        printable characters, up to 40 characters.</p>
1337      </div>
1338    
1339    <div class="section" id="color:syntax-error"><h3>The specified value is not a color
1340      name or hexadecimal color number.</h3></div>
1341    
1342    <div class="section" id="coords:number-not-3"><h3>The <code>coords</code> attribute have to
1343      contain three (3) numbers (specified:
1344      <code><var>{text}</var></code>).</h3></div>
1345    
1346    <div class="section" id="coords:number-not-4"><h3>The <code>coords</code> attribute have to
1347      contain four (4) numbers (specified:
1348      <code><var>{text}</var></code>).</h3></div>
1349    
1350    <div class="section" id="coords:number-lt-6"><h3>The <code>coords</code> attribute have to
1351      contain more than or equal to six (6) numbers (specified:
1352      <code><var>{text}</var></code>).</h3></div>
1353    
1354    <div class="section" id="coords:number-not-even"><h3>The <code>coords</code> attribute have to
1355      contain even number of numbers (specified:
1356      <code><var>{text}</var></code>).</h3></div>
1357    
1358    <div class="section" id="coords:out-of-range"><h3>The specified value <code><var>{value}</var></code>
1359      is out of range.</h3></div>
1360    
1361    <div class="section" id="coords:syntax-error"><h3>The specified value is not valid.</h3></div>
1362    
1363    <div class="section" id="datetime:bad-year"><h3>Year number is out of range.</h3></div>
1364    
1365    <div class="section" id="datetime:bad-month"><h3>Month number is out of range.</h3></div>
1366    
1367    <div class="section" id="datetime:bad-day"><h3>Day number is out of range.</h3></div>
1368    
1369    <div class="section" id="datetime:bad-hour"><h3>Hour number is out of range.</h3></div>
1370    
1371    <div class="section" id="datetime:bad-minute"><h3>Minute number is out of range.</h3></div>
1372    
1373    <div class="section" id="datetime:bad-second"><h3>Second number is out of range.</h3></div>
1374    
1375    <div class="section" id="datetime:bad-timezone-hour"><h3>Hour number of the timezone component is out of
1376      range.</h3></div>
1377    
1378    <div class="section" id="datetime:bad-timezone-minute"><h3>Minute number of the timezone component is out of
1379      range.</h3></div>
1380    
1381    <div class="section" id="datetime:syntax-error"><h3>The attribute value is not a datetime.</h3></div>
1382    
1383    <div class="section" id="dateortime:syntax-error"><h3>The value is not a date or time.</h3></div>
1384    
1385    <div class="section" id="enumerated:invalid"><h3>This attribute only allow a limited set of
1386      values and the specified value <code><var>{@}</var></code> is not one
1387      of them.</h3>
1388        <p>For this attribute only several values are allowed and the
1389        value of the attribute is not one of them.  The document
1390        is non-conforming.</p>
1391    
1392        <dl>
1393        <dt>HTML <code>meta</code> element, <code>http-equiv</code> attribute</dt>
1394            <dd><p>Only values <code>Default-Style</code> and <code>Refresh</code>
1395            are allowed.</p>
1396            <p>Value <code>Content-Type</code> is obsolete; for charset
1397            declaration, the <code>charset</code> attribute can be used as:
1398            <pre class="html example">
1399    <code>&lt;meta charset="<var>charset-name</var>"&gt;</code></pre>
1400            ... where <var>charset-name</var> is a name of the character encoding
1401            of the document, such as <code>utf-8</code>.</p>
1402            <p>Values <code>Content-Style-Type</code> and
1403            <code>Content-Script-Type</code> are currently not allowed.</p>
1404            <p>Value <code>Keywords</code> is not allowed.  Use
1405            <code>name</code> attribute instead of <code>http-equiv</code>
1406            attribute.</p>
1407            <p>Values <code>Expires</code>, <code>Pragma</code>,
1408            and <code>Cache-Control</code> are not allowed;
1409            use <em>real</em> HTTP header fields for cache control.</p></dd>
1410        </dl>
1411      </div>
1412    
1413    <div class="section" id="enumerated:invalid:http-equiv:content-type"><h3>Character encoding declaration syntax
1414      <code class="html bad example">&lt;meta http-equiv="Content-Type" content="text/html; charset=<var>charset-name</var>"&gt;</code>
1415      is obsolete.</h3>
1416        <p>Old long character encoding declaration syntax
1417        <code class="html bad example">&lt;meta http-equiv="Content-Type" content="text/html; charset=<var>charset-name</var>"&gt;</code>
1418        is in use.  The document is non‐conforming.</p>
1419    
1420        <p>The new character encoding declaration syntax is:
1421          <pre class="html example">
1422    <code>&lt;meta charset="<var>charset-name</var>"&gt;</code></pre>
1423        </p>
1424      </div>
1425    
1426    <div class="section" id="enumerated:non-conforming"><h3>Attribute value <code><var>{@}</var></code>
1427      is not allowed.</h3></div>
1428    
1429    <div class="section" id="duplicate-http-equiv"><h3>There is another pragma
1430      <code><var>{value}</var></code>.</h3></div>
1431    
1432    <div class="section" id="duplicate-ID"><h3>This identifier has already been
1433      assigned to another element.</h3></div>
1434    
1435    <div class="section" id="duplicate-token"><h3>The token <code><var>{value}</var></code>
1436      appears in the attribute value twice.</h3></div>
1437    
1438    <div class="section" id="empty-attribute-value"><h3>The attribute value must not be empty.</h3></div>
1439    
1440    <div class="section" id="float:out-of-range"><h3>The specified value is out of range.</h3></div>
1441    
1442    <div class="section" id="float:syntax-error"><h3>The attribute value is not a real
1443      number.</h3></div>
1444    
1445    <div class="section" id="fragment-points-itself"><h3>A fragment identifier references the element
1446      itself.</h3></div>
1447    
1448    <div class="section" id="fragment-points-nothing"><h3>A fragment identifier references no
1449      node.</h3></div>
1450    
1451    <div class="section" id="hashref:syntax-error"><h3>A hash−name reference must start with a
1452      <code>#</code> character.</h3></div>
1453    
1454    <div class="section" id="id-ne-name"><h3>The <code>id</code> attribute value is
1455      different from the <code>name</code> attribute value.</h3></div>
1456    
1457    <div class="section" id="integer:syntax-error"><h3>The attribute value is not an integer.</h3></div>
1458    
1459    <div class="section" id="link-type:bad-context"><h3>The link type <code><var>{value}</var></code>
1460      cannot be specified for this element.</h3>
1461        <p>The specified link type cannot be used for the element.
1462        The document is non-conforming.</p>
1463    
1464        <p>Link types are associated with limited set of elements.
1465        They cannot be used with other elements.</p>
1466    
1467        <p>For example, link type <code>bookmark</code>
1468        can be used with <code>a</code> or <code>area</code> element,
1469        while it cannot be used with <code>link</code> element.</p>
1470      </div>
1471    
1472    <div class="section" id="invalid-attribute-value"><h3>Attribute value <code><var>{@}</var></code>
1473      is not an allowed value.</h3></div>
1474    
1475    <div class="section" id="length:syntax-error"><h3>The attribute value is not a length
1476      value.</h3></div>
1477    
1478    <div class="section" id="link-type:non-conforming"><h3>The link type <code><var>{value}</var></code>
1479      is non-conforming.</h3>
1480        <p>The specified link type is non-conforming, and therefore
1481        the document is non-conforming.</p>
1482    
1483        <dl class="switch">
1484        <dt>Link type <code>contents</code></dt>
1485          <dd>Use link type <code>index</code>.</dd>
1486        <dt>Link type <code>copyright</code></dt>
1487          <dd>Use link type <code>license</code>.</dd>
1488        <dt>Link type <code>home</code></dt>
1489          <dd>Use link type <code>index</code>.</dd>
1490        <dt>Link type <code>previous</code></dt>
1491          <dd>Use link type <code>prev</code>.</dd>
1492        <dt>Link type <code>start</code></dt>
1493          <dd>Use link type <code>first</code>.</dd>
1494        <dt>Link type <code>toc</code> or <code>top</code></dt>
1495          <dd>Use link type <code>index</code>.</dd>
1496        </dl>
1497      </div>
1498    
1499    <div class="section" id="meta-content-type-syntax-error"><h3>The specified value is not a valid as a long
1500      character encoding declaration.</h3></div>
1501    
1502    <div class="section" id="mismatched-charset-name"><h3>The specified character encoding name
1503      <code><var>{value}</var></code> is different from the actual document
1504      character encoding <code><var>{text}</var></code>.</h3>
1505        <p>The specified character encoding name is different from
1506        the character encoding of the document.  The document
1507        is non‐conforming.</p>
1508      </div>
1509    
1510    <div class="section" id="mismatched-charset-name-not-checked"><h3>Whether the specified character encoding name
1511      <code><var>{value}</var></code> matches to the actual character encoding
1512      name cannot be checked since the input is not a byte stream.</h3></div>
1513    
1514    <div class="section" id="mode:syntax-error"><h3>The attribute value is not a valid mode
1515      name.</h3></div>
1516    
1517    <div class="section" id="nninteger:out-of-range"><h3>The specified value is out of range.</h3></div>
1518    
1519    <div class="section" id="nninteger:syntax-error"><h3>The attribute value is not a non‐negative
1520      integer.</h3></div>
1521    
1522    <div class="section" id="no-referenced-map"><h3>The <code>usemap</code> attribute references
1523      no image map.</h3></div>
1524    
1525    <div class="section" id="no-referenced-menu"><h3>The <code>contextmenu</code> attribute references
1526      no menu.</h3></div>
1527    
1528    <div class="section" id="no-referenced-header-cell"><h3>There is no table header cell whose <code>id</code>
1529      is <code><var>{value}</var></code> in the same table.</h3></div>
1530    
1531    <div class="section" id="refresh:syntax-error"><h3>the specified value is not a valid as part
1532      of a <code>Refresh</code> pragma.</h3></div>
1533    
1534    <div class="section" id="repeat:syntax-error"><h3>The attribute value is not an integer or
1535      a string <code>template</code>.</h3></div>
1536    
1537    <div class="section" id="reserved-browsing-context-name"><h3>Browsing context name
1538      <code><var>{@}</var></code> is reserved.</h3>
1539        <p>The specified browsing context name is reserved.
1540        The document is non-conforming.</p>
1541    
1542        <p>Names of browsing contexts starting with <code>_</code>
1543        (<code>U+005F</code> <code class="charname">LOW LINE</code>)
1544        are reserved so that it must not be used.</p>
1545    
1546        <p>Old version of HTML, non-HTML markup languages, and
1547        Web browsers define or implements special reserved
1548        browsing context names <code>_blank</code>,
1549        <code>_main</code>, and <code>_replace</code>.
1550        However, they are <em>not</em> conforming attribute values.</p>
1551      </div>
1552    
1553    <div class="section" id="Reserved-Prefixes-and-Namespace-Names:Name"><h3>Namespace name <code><var>{text}</var></code>
1554      is reserved and cannot be used for an arbitrary prefix.</h3></div>
1555    
1556    <div class="section" id="Reserved-Prefixes-and-Namespace-Names:Prefix"><h3>Namespace prefix <code><var>{text}</var></code>
1557      is reserved and cannot be used for an arbitrary namespace name.</h3></div>
1558    
1559    <div class="section" id="link-type:proposed"><h3>Link type <code><var>{value}</var></code>
1560      is proposed but not accepted yet; it <em>should not</em> be
1561      used until it has been accepted.</h3>
1562        <p>The link type is in the <i>proposed</i> status; it
1563        <em>should not</em> be used until it has been
1564        accepted.</p>
1565    
1566        <p><strong>Warning</strong>: The data served to the
1567        conforming checker might be out of date; it might have already
1568        been accepted or rejected.  The document might or might not be
1569        conforming depending on the status.  See WHATWG Wiki
1570        for the latest information.</p>
1571      </div>
1572    
1573    <div class="section" id="sizes:syntax-error"><h3>The specified value <code><var>{value}</var></code>
1574      is not a valid value.</h3></div>
1575    
1576    <div class="section" id="space-in-ID"><h3>White space characters are not allowed
1577      in the <code>id</code> attribute.</h3></div>
1578    
1579    <div class="section" id="template:not-template"><h3>The node referenced by the <code>template</code>
1580      attribute is not a template.</h3></div>
1581    
1582    <div class="section" id="window-name:empty"><h3>Browsing context name must not be empty.</h3></div>
1583    
1584    <div class="section" id="window-name:reserved"><h3>Browsing context name
1585      <code><var>{value}</var></code> is reserved.</h3></div>
1586    
1587    <div class="section" id="word-not-allowed"><h3>The word <code><var>{value}</var></code> is not
1588      allowed in this attribute.</h3></div>
1589    
1590    <div class="section" id="XML-1.0-NCName:syntax-error"><h3>The specified value is not a legal XML Namespaces
1591      1.0 <code>NCName</code>.</h3></div>
1592    
1593    <div class="section" id="xml:lang-ne-lang"><h3>The value of the <code>xml:lang</code> attribute
1594      is different from the value of the <code>lang</code> attribute.</h3>
1595        <p>The value of the <code>xml:lang</code> attribute (either the
1596        <code>lang</code> attribute in the <code>xml</code> (i.e.
1597        <code>http://www.w3.org/XML/1998/namespace</code>) namespace, or
1598        the <code>xml:lang</code> attribute in no namespace) for the element has
1599        different value than that of the <code>lang</code> attribute in no
1600        namespace.</p>
1601    
1602        <p>For historical reason, there are two attributes applicable to HTML
1603        elements to specify language information of an element: <code>lang</code>
1604        and <code>xml:lang</code>.  In HTML documents, only <code>lang</code>
1605        attribute in no namespace is allowed and take effect; the
1606        <code>xml:lang</code> attribute in no namespace is ignored in HTML
1607        documents.  In XHTML documents, both <code>lang</code> and
1608        <code>xml:lang</code> attributes are allowed.</p>
1609    
1610        <p>In general, <em>only the <code>lang</code> attribute</em> need to be
1611        specified for an element.</p>
1612    
1613        <p>If both <code>lang</code> and <code>xml:lang</code> attributes are
1614        specified on the same element, their values must be the same value.</p>
1615      </div>
1616    
1617  </section>  </section>
1618    
1619  <section id="table-model-errors">  <section id="table-model-errors">
1620  <h2>Table Model Errors</h2>  <h2>Table Model Errors</h2>
1621    
1622  <div class="section table-model-error" id="table:no-cell-in-last-row"><h3>The table has no cell (<code>td</code> or  <div class="section" id="cell-overlapping"><h3>Cell slot (<var>{text}</var>) is filled by
1623      multiple cells.</h3></div>
1624    
1625    <div class="section" id="colspan-creates-column-with-no-anchored-cell"><h3>This <code>colspan</code> attribute
1626      results in creating a table column that does not contain
1627      any cell anchored to it.</h3></div>
1628    
1629    <div class="section" id="column-with-no-anchored-cell"><h3>This column has no anchored cell.</h3></div>
1630    
1631    <div class="section" id="table:no-cell-in-last-row"><h3>The table has no cell (<code>td</code> or
1632    <code>th</code>) in the last row.</h3></div>    <code>th</code>) in the last row.</h3></div>
1633    
1634    <div class="section" id="table:rowspan-extends-table"><h3>This <code>rowspan</code> attribute
1635      results in creating a table row that does not contain
1636      any cell anchored to it.</h3>
1637        <p>The <code>rowspan</code> attribute value of the cell
1638        is so specified that it extends a table in the row axis.
1639        However, the extended row does not contain any cell by itself.
1640        The document is non-conforming.</p>
1641    
1642        <p>For example, the table below is non-conforming:
1643          <pre class="html bad example">
1644    <code>&lt;table&gt;
1645    &lt;tbody&gt;
1646    &lt;tr&gt;&lt;td rowspan=2&gt;&lt;/td&gt;&lt;/tr&gt;
1647    &lt;/tbody&gt;
1648    &lt;/table&gt;</code></pre>
1649        ... since the second row contains only
1650        a cell that spans between first and second rows.</p>
1651      </div>
1652    
1653    <div class="section" id="row-with-no-anchored-cell"><h3>This row has no anchored cell.</h3></div>
1654    
1655    <div class="section" id="rowspan-creates-row-with-no-anchored-cell"><h3>This <code>rowspan</code> attribute
1656      results in creating a table row that does not contain
1657      any cell anchored to it.</h3></div>
1658    
1659    
1660  </section>  </section>
1661    
1662  <section id="imt-warnings">  <section id="imt-warnings">
1663  <h2>Internet Media Type Warnings</h2>  <h2>Internet Media Type Errors</h2>
1664    
1665    <div class="section" id="boundary:syntax-error"><h3>The specified value is not a valid value
1666      as a multipart boundary.</h3></div>
1667    
1668    <div class="section" id="e4x:syntax-error"><h3>The specified value is not a valid value
1669      for the attribute <code>e4x</code>.</h3></div>
1670    
1671    <div class="section" id="IMT:attribute-syntax-error"><h3>The specified value,
1672      <code><var>{value}</var></code>, is syntactically not a valid
1673      attribute name.</h3></div>
1674    
1675    <div class="section" id="IMT:composite"><h3>The specified media type is a composite
1676      type, which is not allowed in this context.</h3></div>
1677    
1678    <div class="section" id="IMT:limited-use-subtype"><h3>An Internet Media Type whose intended usage
1679      is limited use, <code><var>{value}</var></code> is used.</h3></div>
1680    
1681    <div class="section" id="IMT:syntax-error"><h3>The specified value is not an Internet Media
1682      Type.</h3></div>
1683    
1684    <div class="section" id="IMT:obsolete-parameter"><h3>An obsolete parameter
1685      <code><var>{value}</var></code> is used.</h3></div>
1686    
1687    <div class="section" id="IMT:obsolete-subtype"><h3>An obsolete Internet Media Type
1688      <code><var>{value}</var></code> is used.</h3></div>
1689    
1690    <div class="section" id="IMT:parameter-missing"><h3>Parameter <code><var>{text}</var></code> have to
1691      be specified for the Internet Media Type
1692      <code><var>{value}</var></code>.</h3></div>
1693    
1694    <div class="section" id="IMT:parameter-not-allowed"><h3>Parameter <code><var>{value}</var></code> is not
1695      allowed for this Internet Media Type.</h3></div>
1696    
1697    <div class="section" id="IMT:private-subtype"><h3>Use of a private Internet Media Type
1698      <code><var>{value}</var></code> is not encouraged.</h3></div>
1699    
1700    <div class="section" id="IMT:private-type"><h3>Use of a private type
1701      <code><var>{value}</var></code> is not encouraged.</h3></div>
1702    
1703    <div class="section" id="IMT:subtype-syntax-error"><h3>Value <code><var>{value}</var></code> is
1704      syntactically not a valid subtype value of an Internet Media Type.</h3></div>
1705    
1706    <div class="section" id="IMT:type-syntax-error"><h3>Value <code><var>{value}</var></code> is
1707      syntactically not a valid type.</h3></div>
1708    
1709    <div class="section" id="IMT:unknown-parameter"><h3>An unknown parameter <code><var>{value}</var></code>
1710      is used.  The conformance checker cannot determine whether use of this
1711      parameter is valid or not.</h3></div>
1712    
1713  <div class="section should" id="s:IMT:obsolete-subtype"><h3>An <em>obsolete</em> subtype is used.</h3></div>  <div class="section" id="IMT:unknown-subtype"><h3>An unknown Internet Media Type
1714      <code><var>{value}</var></code> is used.  At the time of the update of
1715      the conformance checker's Internet Media Type database, the subtype is
1716      not reigstered to the IANA registry.  The subtype, however, might be
1717      registerd to the IANA registry thereafter.  Please consult the IANA
1718      registry.</h3></div>
1719    
1720  <div class="section should" id="s:IMT:private-subtype"><h3>A private (<code>x-</code> or <code>x.</code>)  <div class="section" id="IMT:unregistered-subtype"><h3>Use of an Internet Media Type
1721    subtype is used.</h3></div>    <code><var>{value}</var></code> is not encouraged since it is not
1722      part of the IANA registry.</h3></div>
1723    
1724  <div class="section should" id="s:IMT:unregistered-subtype"><h3>The subtype is not registered to IANA.</h3></div>  <div class="section" id="IMT:unregistered-type"><h3>Use of a type
1725      <code><var>{value}</var></code> is not encouraged since it is not
1726      a standardized type.</h3></div>
1727    
1728    <div class="section" id="not-IMT"><h3>A value that is not an Internet Media Type
1729      is not allowed here.</h3></div>
1730    
1731  </section>  </section>
1732    
1733  <section id="uri-errors">  <section id="uri-errors">
1734  <h2>URI (or IRI) Errors</h2>  <h2>URL Errors</h2>
1735    
1736    <div class="section" id="syntax-error:iri3987"><h3>The specified value is syntactically not an
1737      IRI.</h3></div>
1738    
1739    <div class="section" id="syntax-error:iriref3987"><h3>The specified value is syntactically not an IRI
1740      reference.</h3>
1741        <p>The specified value does not satisfy the syntactical requirements
1742        for IRI references.  The document is non-conforming.</p>
1743    
1744        <p>Possible causes:
1745          <ul>
1746          <li>The string might contain one or more white space characters.
1747          Especially, the <code> </code> (<code>U+0020</code>
1748          <code class="charname">SPACE</code>) character cannot be
1749          used in IRI references.</li>
1750          </ul>
1751        </p>
1752      </div>
1753    
1754    <div class="section" id="syntax-error:rdfuriref"><h3>The specified value is syntactically not an RDF
1755      URI reference.</h3></div>
1756    
1757    <div class="section" id="syntax-error:uri2396"><h3>The specified value is syntactically not a
1758      URI according to RFC 2396.</h3></div>
1759    
1760    <div class="section" id="syntax-error:uri3986"><h3>The specified value is syntactically not a
1761      URI.</h3></div>
1762    
1763    <div class="section" id="URL:address-format"><h3>URL host address format
1764      <code><var>{text}</var></code> is not defined.</h3></div>
1765    
1766    <div class="section" id="URL:default-port"><h3>Default port number should be omitted.</h3></div>
1767    
1768    <div class="section" id="URL:dot-segment"><h3>A dot-segment (<code>.</code> or
1769      <code>..</code>) occurs in an absolute reference.</h3>
1770        <p>Dot-segment (<code>.</code> or <code>..</code>) should
1771        not occur in an absolute reference.</p>
1772    
1773        <p>In relative references, dot-segments are used to represent
1774        the current (<code>.</code>) or the parent (<code>..</code>)
1775        hierarchy of the path.  Though they are also allowed
1776        in absolute references, it should be resolved to the
1777        canonical form before it has been published.</p>
1778      </div>
1779    
1780    <div class="section" id="URL:empty-host"><h3>The host component of the URL is empty.</h3></div>
1781    
1782    <div class="section" id="URL:empty-path"><h3>The URL does not end with
1783      a <code>/</code> character.</h3></div>
1784    
1785    <div class="section" id="URL:empty-port"><h3>The port component of the URL is empty.</h3></div>
1786    
1787    <div class="section" id="URL-fragment-not-allowed"><h3>The fragment component of the URL is not
1788      allowed.</h3></div>
1789    
1790    <div class="section" id="URL:long-host"><h3>The host component of the URL
1791      is too long.</h3></div>
1792    
1793    <div class="section" id="URL:lowercase-hexadecimal-digit"><h3>A lowercase hexadecimal digit is used
1794      in percent-encoding.</h3>
1795        <p>The hexadecimal digit in percent-encoding string in the IRI
1796        is in lowercase.  Though the IRI <em>is</em> conforming,
1797        it should be in uppercase.</p>
1798      </div>
1799    
1800  <div class="section must" id="m:URI::syntax-error"><h3>This string is not an IRI syntactically.</h3></div>  <div class="section" id="URL:non-DNS-host"><h3>The host component of the URL
1801      is not a DNS host name.</h3></div>
1802    
1803    <div class="section" id="URL:non-UTF-8-host"><h3>The host component of the URL
1804      is not encoded in UTF-8.</h3></div>
1805    
1806    <div class="section" id="URL:password"><h3>Password should not be included in a URL
1807      for the security.</h3></div>
1808    
1809    <div class="section" id="URL:percent-encoded-unreserved"><h3>An unreserved character is
1810      percent-encoded.</h3>
1811        <p>An unreserved character is percent-encoded in the IRI.
1812        Though it <em>is</em> conforming, it should be in the
1813        decoded (or bare) form.</p>
1814      </div>
1815    
1816    <div class="section" id="URL:uppercase-host"><h3>The host <code><var>{value}</var></code>
1817      should be spelt in lowercase.</h3></div>
1818    
1819    <div class="section" id="URL:uppercase-scheme-name"><h3>URL scheme name is in uppercase.</h3>
1820        <p>The scheme part of the IRI is written in uppercase letter.</p>
1821    
1822        <p>Uppercase scheme names are not required to be processed
1823        correctly.</p>
1824    <!-- @@
1825     RFC 3986 3.1.
1826     > Although schemes are case-
1827       insensitive, the canonical form is lowercase and documents that
1828       specify schemes must do so with lowercase letters.
1829    
1830     > An implementation ... should only produce lowercase scheme names for
1831       consistency.
1832    -->
1833      </div>
1834    
1835  </section>  </section>
1836    
1837  <section id="uri-errors">  <section id="mq-errors">
1838  <h2>URI (or IRI) Errors</h2>  <h2>Media Query Errors</h2>
1839    
1840    <div class="section" id="mq-syntax-error"><h3>The specified value has a syntax error as a
1841      media query.</h3></div>
1842    
1843    <div class="section" id="unknown-media-type"><h3>Media type <code><var>{value}</var></code> is
1844      not supported by the conformance checker.</h3></div>
1845    
1846    </section>
1847    
1848    <section id="selectors-errors">
1849    <h2>Selectors Errors</h2>
1850    
1851    <div class="section" id="an+b-not-closed"><h3>Argument list of the pseudo-class is
1852      not closed by a <code>)</code> character.</h3></div>
1853    
1854    <div class="section" id="ab+b-not-integer"><h3>Numbers in the argument
1855      <code><var>a</var>n+<var>b</var></code> have to be integers.</h3></div>
1856    
1857    <div class="section" id="an+b-syntax-error"><h3>Argument <code><var>a</var>n+<var>b</var></code> is
1858      syntactically incorrect.</h3></div>
1859    
1860    <div class="section" id="attr-selector-not-closed"><h3>Attribute selector is not closed by
1861      a <code>]</code> character.</h3></div>
1862    
1863    <div class="section" id="lang-selector-not-closed"><h3>Argument list of the <code>:lang</code>
1864      selector is not closed by a <code>)</code> character.</h3></div>
1865    
1866    <div class="section" id="namespace-prefix:not-declared"><h3>Namespace prefix <code><var>{value}</var></code>
1867      is not declared.</h3></div>
1868    
1869    <div class="section" id="no-attr-local-name"><h3>Attribute local name is missing.</h3></div>
1870    
1871    <div class="section" id="no-attr-match"><h3>Attribute matching operator (e.g.
1872      <code>=</code>) is missing.</h3></div>
1873    
1874  <div class="section should" id="s:URI::empty-path"><h3>This IRI should explicitly end with  <div class="section" id="no-attr-name"><h3>Attribute name is missing.</h3></div>
1875    <code>/</code>.</h3></div>  
1876    <div class="section" id="no-attr-namespace-separator"><h3>Attribute namespace wildcard <code>*</code>
1877      is not followed by a <code>|</code> character.</h3></div>
1878    
1879    <div class="section" id="no-attr-value"><h3>Attribute value is missing.</h3></div>
1880    
1881    <div class="section" id="no-class-name-selector"><h3>Class name is missing.</h3></div>
1882    
1883    <div class="section" id="no-combinator"><h3>Combinator is missing.</h3></div>
1884    
1885    <div class="section" id="no-contains-string"><h3>No string is specified in the argument
1886      list of the <code>:-manakai-contains</code> pseudo-class
1887      selector.</h3></div>
1888    
1889    <div class="section" id="no-lang-tag"><h3>Language tag argument is missing.</h3></div>
1890    
1891    <div class="section" id="no-local-name-selector"><h3>Local name part of the type selector (or
1892      <code>*</code> for the universal selector) is missing.</h3></div>
1893    
1894    <div class="section" id="no-pseudo-class-name"><h3>Pseudo-class name is missing.</h3></div>
1895    
1896    <div class="section" id="no-pseudo-element-name"><h3>Pseudo-element name is missing.</h3></div>
1897    
1898    <div class="section" id="no-sss"><h3>Sequence of simple selectors is
1899      expected.</h3></div>
1900    
1901    <div class="section" id="not-not-closed"><h3>Argument list of the <code>:not</code> selector
1902      is not closed by a <code>)</code> character.</h3></div>
1903    
1904    <div class="section" id="ss-after-pseudo-element"><h3>Simple selector is not allowed after a
1905      pseudo element.</h3></div>
1906    
1907    <div class="section" id="unknown-pseudo-class"><h3>Pseudo-class <code>:<var>{value}</var></code>
1908      is not supported by the conformance checker.</h3></div>
1909    
1910    <div class="section" id="unknown-pseudo-element"><h3>Pseudo-element <code>::<var>{value}</var></code>
1911      is not supported by the conformance checker.</h3></div>
1912    
1913    </section>
1914    
1915    <section id="css-errors">
1916    <h2>CSS Errors</h2>
1917    
1918    <div class="section" id="at-rule-not-allowed"><h3>An <code>@<var>{text}</var></code> rule is not
1919      allowed here.</h3></div>
1920    
1921    <div class="section" id="at-rule-syntax-error"><h3>The <code>@<var>{text}</var></code> rule is
1922      syntactically incorrect.</h3></div>
1923    
1924    <div class="section" id="block-not-closed"><h3>Block is not closed before the end of
1925      file.</h3></div>
1926    
1927    <div class="section" id="CSS-duplication"><h3>Component <code>&lt;<var>{text}</var>&gt;</code> is
1928      already specified.</h3></div>
1929    
1930    <div class="section" id="CSS-cursor-hand"><h3>Value <code>hand</code> is not valid as
1931      <code>&lt;'cursor'&gt;</code>.</h3></div>
1932    
1933    <div class="section" id="CSS-syntax-error"><h3>Specified value is syntactically not a correct
1934      <code>&lt;<var>{text}</var>&gt;</code>.</h3></div>
1935    
1936    <div class="section" id="no-declaration-block"><h3>No declaration block is found after a group of
1937      selectors.</h3></div>
1938    
1939    <div class="section" id="no-property-colon"><h3>A <code>:</code> character is missing after
1940      a property name.</h3></div>
1941    
1942    <div class="section" id="no-property-name"><h3>Property name is expected.</h3></div>
1943    
1944    <div class="section" id="no-property-semicolon"><h3>A <code>;</code> character is missing at the
1945      end of the property.</h3></div>
1946    
1947    <div class="section" id="priority-syntax-error"><h3>Priority part of the declaration is syntactically
1948      incorrect.</h3></div>
1949    
1950    <div class="section" id="unknown-at-rule"><h3>The <code>@<var>{value}</var></code> rule is
1951      not supported by the conformance checker.</h3></div>
1952    
1953    <div class="section" id="unknown-property"><h3>Property <code><var>{value}</var></code> is
1954      not supported by the conformance checker.</h3></div>
1955    
1956    </section>
1957    
1958    <section id="cache-manifest-errors">
1959    <h2>Cache Manifest Errors</h2>
1960    
1961    <div class="section" id="both-in-entries-and-whitelist"><h3>This URL is found both in the explicit or
1962      fallback entries and in the online whitelist.</h3></div>
1963    
1964    <div class="section" id="different-origin-from-manifest"><h3>The specified URL has different origin from
1965      the manifest.</h3></div>
1966    
1967    <div class="section" id="different-scheme-from-manifest"><h3>The scheme component of the URL is
1968      different from that of the manifest URL.  The URL is ignored.</h3></div>
1969    
1970    <div class="section" id="duplicate-oc-namespace"><h3>This oppotunistic caching namespace is already
1971      specified.</h3></div>
1972    
1973    <div class="section" id="no-fallback-entry-URL"><h3>Fallback entry URL is missing.</h3></div>
1974    
1975    <div class="section" id="not-manifest"><h3>This document is not a cache manifest.</h3>
1976        <p>The specified document is <em>not</em> a cache manifest.
1977        The document is non-conforming.</p>
1978    
1979        <p>An entity labeled as Internet media type
1980        <code>text/cache-manifest</code> must contain a cache manifest.</p>
1981    
1982        <p>A cache manifest must start with a line whose content is
1983        <code class="manifest example">CACHE MANIFEST</code>
1984        (exactly one space character between
1985        <code>CACHE</code> and <code>MANIFEST</code>).</p>
1986      </div>
1987    
1988    <div class="section" id="same-as-manifest-URL"><h3>This URL is same as the manifest URL.</h3></div>
1989    
1990    </section>
1991    
1992    <section id="information">
1993    <h2>Stability Information</h2>
1994    
1995    <div class="section" id="deprecated:attr"><h3>This attribute is deprecated.</h3></div>
1996    
1997    <div class="section" id="deprecated:element"><h3>This element is deprecated.</h3></div>
1998    
1999    <div class="section" id="status:cr:element"><h3>This element is in the
2000      <strong>call for implementation</strong> stage.</h3>
2001        <p>The element is in the call for implementation stage.</p>
2002        
2003        <p>Usually, using the element is safe.  However, it is a new feature
2004        so that it might not be implemented correctly.  If it is found that
2005        the feature is hard or impossible to implement, the feature
2006        might be revised, or in some case it might be dropped.</p>
2007    
2008        <p>Elements defined by Atom 1.0 (IETF Proposed Standard), and XBL 2.0
2009        (W3C Candidate Recommendation) belong to this class.</p>
2010      </div>
2011    
2012    <div class="section" id="status:lc:element"><h3>This element is in the <strong>last
2013      call for comments</strong> stage.</h3>
2014        <p>The element is in the last call for comments stage.</p>
2015        
2016        <p>The element is relatively mature, though the standardization
2017        is not done yet.  It may be used for experiments.  Since it is a new
2018        feature, it might not be implemented correctly or at all.  If it is
2019        found that the feature is hard or impossible to implement, the feature
2020        might be revised or might be dropped.</p>
2021    
2022        <p>Elements defined by Web Forms 2.0 as well as some elements
2023        defined by HTML5 belong to this class.</p>
2024      </div>
2025    
2026    <div class="section" id="status:wd:element"><h3>This element is documented in a <strong>working
2027      draft</strong>.</h3>
2028        <p>The element is documented in a working or editor's draft
2029        and not yet completed.</p>
2030        
2031        <p>The element should not be used for any practical purpose.
2032        The feature might be drastically changed later or might be
2033        entirely removed.</p>
2034    
2035        <p>Most of new elements defined by HTML5 belong to this class.</p>
2036      </div>
2037    
2038    <div class="section" id="status:non-standard:element"><h3>This element is <strong>not part of any
2039      standard</strong> the conformance checker knows.</h3>
2040        <p>The element is not part of any standard or draft the conformance
2041        checker is aware of.</p>
2042        
2043        <p>The element should not be used for any practical purpose unless
2044        there is really a standard that defines the element.</p>
2045      </div>
2046    
2047    <div class="section" id="status:cr:attr"><h3>This attribute is in the
2048      <strong>call for implementation</strong> stage.</h3>
2049        <p>The attribute is in the call for implementation stage.</p>
2050        
2051        <p>Usually, using the attribute is safe.  However, it is a new feature
2052        so that it might not be implemented correctly.  If it is found that
2053        the feature is hard or impossible to implement, the feature
2054        might be revised, or in some case it might be dropped.</p>
2055      </div>
2056    
2057    <div class="section" id="status:lc:attr"><h3>This attribute is in the <strong>last
2058      call for comments</strong> stage.</h3>
2059        <p>The attribute is in the last call for comments stage.</p>
2060        
2061        <p>The attribute is relatively mature, though the standardization
2062        is not done yet.  It may be used for experiments.  Since it is a new
2063        feature, it might not be implemented correctly or at all.  If it is
2064        found that the feature is hard or impossible to implement, the feature
2065        might be revised or might be dropped.</p>
2066      </div>
2067    
2068    <div class="section" id="status:wd:attr"><h3>This attribute is documented in a <strong>working
2069      draft</strong>.</h3>
2070        <p>The attribute is documented in a working or editor's draft
2071        and not yet completed.</p>
2072        
2073        <p>The attribute should not be used for any practical purpose.
2074        The feature might be drastically changed later or might be
2075        entirely removed.</p>
2076      </div>
2077    
2078    <div class="section" id="status:non-standard:attr"><h3>This attribute is <strong>not part of any
2079      standard</strong> the conformance checker knows.</h3>
2080        <p>The attribute is not part of any standard or draft the conformance
2081        checker is aware of.</p>
2082        
2083        <p>The attribute should not be used for any practical purpose unless
2084        there is really a standard that defines the attribute.</p>
2085      </div>
2086    </section>
2087    
2088    <section id="langtag-errors">
2089    <h2>Language Tag Errors</h2>
2090    
2091    <div class="section" id="langtag:extension:duplication"><h3>There is another extension subtag
2092      <code><var>{value}</var></code>.</h3></div>
2093    
2094    <div class="section" id="langtag:illegal"><h3>Subtag <code><var>{value}</var></code> is
2095      syntactically invalid.</h3></div>
2096    
2097    <div class="section" id="langtag:language:case"><h3>It is a good practice to represent ISO 639-1
2098      language code <code><var>{value}</var></code> in lowercase.</h3></div>
2099    
2100    <div class="section" id="langtag:language:mul"><h3>Langauge tag <code>mul</code> should not be
2101      used.</h3></div>
2102    
2103    <div class="section" id="langtag:language:nosemantics"><h3>No semantics is defined for language subtag
2104      <code><var>{value}</var></code>.</h3></div>
2105    
2106    <div class="section" id="langtag:language:syntax"><h3>The language subtag <code><var>{value}</var></code>
2107      is syntactically invalid.</h3></div>
2108    
2109    <div class="section" id="langtag:language:und"><h3>Langauge tag <code>und</code> should not be
2110      used.</h3></div>
2111    
2112    <div class="section" id="langtag:private"><h3>It would be better if a private use language
2113      tag (<code><var>{value}</var></code>) is not used.</h3></div>
2114    
2115    <div class="section" id="langtag:privateuse:syntax"><h3>Private use subtag <code><var>{value}</var></code>
2116      is syntactically invalid.</h3></div>
2117    
2118    <div class="section" id="langtag:region:case"><h3>It is a good practice to represent ISO 3166
2119      country code <code><var>{value}</var></code> in uppercase.</h3></div>
2120    
2121    <div class="section" id="langtag:region:nosemantics"><h3>No semantics is defined for region subtag
2122      <code><var>{value}</var></code>.</h3></div>
2123    
2124    <div class="section" id="langtag:region:private"><h3>Use of private use country code
2125      <code><var>{value}</var></code> is not allowed.</h3></div>
2126    
2127    </section>
2128    
2129    <section id="rdfxml-errors">
2130    <h2>RDF/XML Errors</h2>
2131    
2132    <div class="section" id="bad-rdf-namespace"><h3>The namespace URI of an element that
2133      represents an RDF concept must be
2134      <code>http://www.w3.org/1999/02/22-rdf-syntax-ns#</code>.</h3></div>
2135    
2136    <div class="section" id="duplicate-rdf-id"><h3>The specified value is already used as an
2137      ID.</h3></div>
2138    
2139    <div class="section" id="duplicate-unqualified-attr"><h3>Both unqualified attribute and namespace‐qualified
2140      RDF attribute are specified, which is not allowed.</h3></div>
2141    
2142    <div class="section" id="parse-type-other"><h3>An invalid value is specified to
2143      the <code>parseType</code> attribute.</h3></div>
2144    
2145    <div class="section" id="second-node-element"><h3>There is another element, such that
2146      this element is not allowed.</h3></div>
2147    
2148    <div class="section" id="unqualified-attr"><h3>Unqualified attribute is not allowed.</h3></div>
2149    
2150    <div class="section" id="unqualified-rdf-attr"><h3>RDF attribute should be
2151      namespace‐qualified.</h3></div>
2152    
2153  </section>  </section>
2154    
2155  <section id="unsupported-messages">  <section id="unsupported-messages">
2156  <h2><i>Unsupported</i> Messages</h2>  <h2><i>Unsupported</i> Messages</h2>
2157    
2158  <div class="section unsupported" id="unsupported:attribute"><h3>This attribute is not supported by the  <div class="section" id="unknown-element"><h3>Conformance checking for element
2159    conformance checker; <em>it might or might not be conforming</em>.</h3>    <code><var>{local-name}</var></code> is not supported; <em>it might or
2160      <p>The conformant checker does not support the attribute.    might not be conforming</em>.</h3>
2161        <p>The conformant checker does not support the element.
2162      It cannot determine whether the document is conforming or not.</p>      It cannot determine whether the document is conforming or not.</p>
2163    </div>    </div>
2164    
2165  <div class="section unsupported" id="unsupported:element"><h3>This element is not supported by the  <div class="section" id="unknown-attribute"><h3>Conformance checking for attribute
2166    conformance checker; <em>it might or might not be conforming</em>.</h3>    <code><var>{local-name}</var></code> of element
2167      <p>The conformant checker does not support the element.    <code><var>{element-local-name}</var></code> is not supported;
2168      <em>it might or might not be conforming</em>.</h3>
2169        <p>The conformant checker does not support the attribute.
2170      It cannot determine whether the document is conforming or not.</p>      It cannot determine whether the document is conforming or not.</p>
2171    </div>    </div>
2172    
2173  <div class="section unsupported" id="unsupported:link-type"><h3>The link type <code>$0</code> is not standardized  <div class="section" id="unknown-link-type"><h3>Link type <code><var>{value}</var></code> is not
2174    or registered at the time of the release of the conformance checker;    standardized or registered at the time of the release of the conformance
2175    <em>it is non-conforming unless it has now been registered</em>.</h3>    checker; <em>it is non-conforming unless it now has been
2176      registered</em>.</h3>
2177      <p>The <code>rel</code> attribute is defined as a list of link types.      <p>The <code>rel</code> attribute is defined as a list of link types.
2178      Some common link types are defined in the HTML5 specification.      Some common link types are defined in the HTML5 specification.
2179      Additional link types can be registered to the WHATWG Wiki.      Additional link types can be registered to the WHATWG Wiki.
# Line 217  Web Document Conformance Checker (BETA)< Line 2184  Web Document Conformance Checker (BETA)<
2184      The link type might have been added to the registry since then.      The link type might have been added to the registry since then.
2185      In such case it might be conforming.  Otherwise, the      In such case it might be conforming.  Otherwise, the
2186      document is non-conforming.</p>      document is non-conforming.</p>
2187    
2188        <dl>
2189        <dt>Link types <code>shortcut icon</code></dt>
2190            <dd>Link type <code>shortcut</code> is not registered.
2191            Use only <code>icon</code> for linking to so-called favicon.</dd>
2192        </dl>
2193      </div>
2194    
2195    <div class="section" id="event-handler"><h3>Conformance checking for event handler attribute
2196      is not supported; <em>it might or might not be conforming.</em></h3></div>
2197    
2198    <div class="section" id="media-query"><h3>Conformance checking for media query
2199      is not supported; <em>it might or might not be conforming.</em></h3></div>
2200    
2201    <div class="section" id="addr-spec-not-supported"><h3>Conformance checking for an <code>addr-spec</code>
2202      is not supported; <em>it might or might not be conforming.</em></h3></div>
2203    
2204    <div class="section" id="XML-script-lang"><h3>Conformance checking for script
2205      language <code><var>{text}</var></code> is not supported;
2206      <em>it might or might not be conforming.</em></h3></div>
2207    
2208    <div class="section" id="XML-style-lang"><h3>Conformance checking for style
2209      language <code><var>{text}</var></code> is not supported;
2210      <em>it might or might not be conforming.</em></h3></div>
2211    
2212    <div class="section" id="atom|content-not-supported"><h3>Conformance checking for an Atom
2213      <code>content</code> element with <code>type</code>
2214      <code><var>{text}</var></code> is not supported.</h3></div>
2215    
2216    <div class="section" id="help-not-available"><h3>No more information is available.</h3>
2217        <p>No more information is available for this topic.</p>
2218    </div>    </div>
2219    
2220  </section>  </section>
2221    
2222  <d:catalog>  
2223  manakaiCompatMode:quirks;;Quirks Mode  
2224  manakaiCompatMode:limited quirks;;Limited Quirks Mode  
2225  manakaiCompatMode:no quirks;;No Quirks Mode  
2226    
2227  manakaiIsHTML:1;;HTML Document  
2228  manakaiIsHTML:0;;XML Document  
2229  </d:catalog>  
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2429    
2430    <div class="section" id="Error-level-m"><h3><a href="../error-description#Error-level-m" rel="help"><em class="rfc2119">MUST</em>‐level
2431            error</a></h3>
2432        <p>A violation to a hard requirement of the specification.
2433        The document is non‐conforming.</p>
2434      </div>
2435    
2436    <div class="section" id="Error-level-s"><h3><a href="../error-description#Error-level-s" rel="help"><em class="rfc2119">SHOULD</em>‐level
2437            error</a></h3>
2438        <p>A violation to a requirement of the specification.
2439        The violation might be legitimize in some case.  Otherwise,
2440        the document is non‐conforming.</p>
2441      </div>
2442    
2443    <div class="section" id="Error-level-w"><h3><a href="../error-description#Error-level-w" rel="help">Warning</a></h3>
2444        <p>A warning is an advice from the conformance checker
2445        to avoid solving a problem in a confusing or possibly wrong way.
2446        It does not affect to the conformance of the document, and
2447        may sometimes be inappropriate.</p>
2448      </div>
2449    
2450    <div class="section" id="Error-level-i"><h3><a href="../error-description#Error-level-i" rel="help">Information</a></h3>
2451        <p>An informational message just provides an additional information
2452        on the feature used in the document or the status of the retrieval
2453        or so on.
2454        It does not affect to the conformance of the document.</p>
2455      </div>
2456    
2457    <div class="section" id="Error-level-u"><h3><a href="../error-description#Error-level-u" rel="help">Not
2458          supported</a></h3>
2459        <p>Some feature that is not supported by the conformance checker
2460        is used in the document.</p>
2461      </div>
2462    
2463  <section id="license">  <section id="license">
2464  <h2>License of This Document</h2>  <h2>License of This Document</h2>
2465    
2466  <p>Copyright 2007 <a href="http://suika.fam.cx/~wakaba/who?">Wakaba</a></p>  <p>Copyright <time>2007</time>‐<time>2008</time>
2467  <p>This library is free software; you can redistribute it  <a href="http://suika.fam.cx/~wakaba/who?" rel="author" xml:lang="ja">Wakaba</a>
2468    <code class="mail">&lt;<a href="mailto:[email protected]">[email protected]</a>&gt;</code>.</p>
2469    
2470    <p>This document is free software; you can redistribute it
2471  and/or modify it under the same terms as Perl itself.</p>  and/or modify it under the same terms as Perl itself.</p>
2472  </section>  </section>
2473    
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