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revision 1.1 by wakaba, Sun Jul 1 10:02:24 2007 UTC revision 1.27 by wakaba, Fri Aug 15 14:11:13 2008 UTC
# Line 8  Web Document Conformance Checker (BETA)< Line 8  Web Document Conformance Checker (BETA)<
8  <body>  <body>
9  <h1>Description of Errors</h1>  <h1>Description of Errors</h1>
10    
11  <section id="html5-parse-errors">  <section id="character-encoding-layer">
12  <h2>HTML5 Parse Errors</h2>  <h2>Character Encoding Layer Errors</h2>
13    
14  <div class="section parse-error" id="after-head"><h3>The <code><var>$0</var></code> element cannot be  <div class="section error-category-charset" id="m:illegal-octets-error"><h3>An illegal octet in the input stream.</h3></div>
15    inserted between <code>head</code> and <code>body</code> elements.</h3>  </section>
16      <p>A start tag occurs after the <code>head</code> element is closed  
17      but before the <code>body</code> element is opened.  <section id="html5-character-encoding">
18    <h2>HTML5 Character Encoding Errors</h2>
19    
20    <div class="section " id="disallowed-character-encoding"><h3>Character encoding <code><var>{text}</var></code>
21      is not allowed for <abbr>HTML</abbr> document.</h3>
22        <p>The character encoding used for the document is not allowed
23        for <abbr>HTML</abbr> document.  The document is non‐conforming.</p>
24      </div>
25    
26    <div class="section " id="bad-character-encoding"><h3>Character encoding <code><var>{text}</var></code>
27      should not be used for <abbr>HTML</abbr> document.</h3>
28        <p>The character encoding used for the document is not recommended
29        for <abbr>HTML</abbr> document.  The document is non‐conforming
30        unless there is any good reason to use that encoding.</p>
31      </div>
32    
33    <div class="section " id="non-utf-8-character-encoding"><h3>Use of UTF-8 is encouraged (this document
34      is encoded in <code><var>{text}</var></code>).</h3>
35        <p>Use of UTF-8 as the character encoding of the document is encouraged,
36        though the use of another character encoding is still conforming.</p>
37      </div>
38    
39    <div class="section " id="character-encoding-unchecked"><h3>Conformance for character encoding requirements
40      cannot be checked, since the input is not a byte stream.</h3>
41        <p>The conformance checker cannot detect whether the input document
42        met the requirements on character encoding, since the document
43        is not inputed as a serialized byte sequence.  The document is
44        not conforming if it is not encoded in an appropriate character
45        encoding with appropriate labeling.</p>
46      </div>
47    
48    <div class="section " id="no-character-encoding-declaration"><h3>There is no character encoding
49      declaration.</h3>
50        <p>The document does not contain a character encoding
51        declaration.  Unless the character encoding is explicitly
52        specified in lower‐level protocol, e.g. in <abbr>HTTP</abbr>,
53        or is implied by <abbr>BOM</abbr>, there must be a character
54        encoding declaration.  The document is non‐conforming.</p>
55    
56        <p>The long character encoding declaration syntax
57        <code class="html bad example">&lt;meta http-equiv="Content-Type" content="text/html; charset=<var>charset-name</var>"&gt;</code>
58        is obsolete.  The new syntax is:</p>
59        <pre class="html example">
60    <code>&lt;meta charset="<var>charset-name</var>"&gt;</code></pre>
61    
62        <p>Note that the <code>encoding</code> declaration in <abbr>XML</abbr>
63        declaration has no effect for <abbr>HTML</abbr> document.</p>
64      </div>
65    
66    <div class="section " id="non-ascii-superset"><h3>No character encoding metadata is found
67      in lower‐level protocol nor is there <abbr>BOM</abbr>, while
68      character encoding <code><var>{text}</var></code>
69      is not a superset of <abbr>ASCII</abbr>.</h3>
70        <p>The document is not labeled with character encoding name
71        in lower‐level protocol, e.g. in <abbr>HTTP</abbr>, and
72        the document is not begin with <abbr>BOM</abbr>.  In addition,
73        the character encoding of the document is not a superset of
74        <abbr>ASCII</abbr>.  The document is non‐conforming.</p>
75    
76        <p>Unless there is a <abbr>BOM</abbr>, the character encoding
77        for the document must be specified in e.g. <abbr>HTTP</abbr>‐level,
78        as:</p>
79        <pre class="http example">
80    <code>Content-Type: text/html; charset=<var>charset-name</var></code></pre>
81    
82        <p>Existence of <abbr>HTML</abbr> character encoding declaration, i.e.
83        <code class="html example">&lt;meta charset="<var>charset-name</var>"&gt;</code>,
84        does not allow to omit <code>charset</code> parameter
85        for <abbr>HTML</abbr> document encoded in non‐<abbr>ASCII</abbr>
86        compatible encoding.</p>
87    
88        <p>Character encodings <code>Shift_JIS</code>, <code>Windows-31J</code>,
89        and <code>ISO-2022-JP</code> are <em>not</em> a superset of
90        <abbr>ASCII</abbr> for the purpose of <abbr>HTML</abbr> conformance.</p>
91      </div>
92    
93    <div class="section " id="sniffing:chardet"><h3>Character encoding of this document is sniffed
94      as <code><var>{text}</var></code> (Sniffed because no explicit specification
95      for the character encoding of this document is found in the transfer
96      procotol headers).</h3></div>
97    
98    <div class="section " id="sniffing:default"><h3>Character encoding of this document is defaulted
99      to <code><var>{text}</var></code> because no explicit specification
100      for the character encoding of this document is found in the transfer
101      procotol headers.</h3></div>
102    
103    <div class="section " id="chardecode:fallback"><h3>Since no decoder for the document character
104      encoding is found, decoder for the character encoding
105      <code><var>{text}</var></code> is used.  Checking results might be
106      <em>wrong</em>.</h3></div>
107    
108    <div class="section " id="chardecode:no-error"><h3>Conformance error checking for the character
109      encoding <code><var>{text}</var></code> is not supported.</h3></div>
110    
111    <div class="section " id="charset-label:matching"><h3>Sniffed character encoding
112      <code><var>{text}</var></code> is same as the character encoding specified
113      in the character encoding declaration.  This is <em>not</em> an
114      error.</h3></div>
115    
116    <div class="section format-charset warning" id="charset-label-detected"><h3>While parsing the document as
117      <code><var>{text}</var></code>, a character encoding declaration specifying
118      a different character encoding is found.  The document
119      is reparsed.</h3>
120        <p>While parsing a document in a character encoding,
121        a character encoding declaration which declares the character
122        encoding of the document as another character encoding is found.
123        The occurence of this warning itself does not make the document
124        non‐conforming.  However, the failure of the first attempt to
125        to detect the character encoding might be a result of non‐conformance
126        of the document.</p>
127    
128        <p>The document will be reparsed from the beginning.  Some error
129        or warning might be reported again.</p>
130    
131        <p>These are suggestions to avoid this warning:</p>
132        <ul>
133        <li>Specify <code>charset</code> parameter in the <code>Content-Type</code>
134        field in the <abbr>HTTP</abbr> header, as:
135        <pre class="HTTP example">
136    <code>Content-Type: text/html; charset="<var>charset-name</var>"</code></pre></li>
137        <li>Put the character encoding declaration
138        (<code class="html example">&lt;meta charset="<var>charset-name</var>"&gt;</code>)
139        just after <code class="html example">&lt;head&gt;</code> start tag.</li>
140        <li>Use <code>UTF-8</code>.</li>
141        </ul>
142      </div>
143    
144    <div class="section " id="NULL"><h3>The <code class="charname">NULL</code> character
145      is not allowed.</h3></div>
146    
147    <div class="section " id="control-char"><h3>Code point <code><var>{text}</var></code> is
148      not allowed.</h3></div>
149    
150    </section>
151    
152    <section id="html5-tokenize-error">
153    <h2>HTML5 Parse Errors in Tokenization Stage</h2>
154    
155    <div class="section parse-error" id="after-html"><h3>Tag <code>&lt;<var>$0</var>&gt;</code>
156      is not allowed after the end tag <code>&lt;/html&gt;</code>.</h3>
157        <p>The start or end tag of an element appears after the
158        <code>html</code> element has been closed.  The document is
159        non-conforming.</p>
160    
161        <p>Any content of the document other than comments
162        must be put into the <code>html</code> element.</p>
163      </div>
164    
165    <div class="section parse-error" id="after-body"><h3>Tag <code>&lt;<var>$0</var>&gt;</code>
166      is not allowed after the end tag <code>&lt;/body&gt;</code>.</h3>
167        <p>The start or end tag of an element appears after the
168        <code>body</code> element has been closed.  The document is
169        non-conforming.</p>
170    
171        <p>Any content of the document other than <code>head</code>
172        contents and comments must be put into the <code>body</code>
173        element.</p>
174      </div>
175    
176    <div class="section tokenize-error" id="bad-attribute-name"><h3>Attribute name cannot contain characters
177      <code>"</code>, <code>'</code>, and <code>=</code>.</h3></div>
178    
179    <div class="section tokenize-error" 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></div>
182    
183    <div class="section tokenize-error" id="bare-ero"><h3>The <code>&amp;</code> character must
184      be escaped as <code class="html example">&amp;amp;</code>.</h3>
185        <p>An <code>&amp;</code> character which
186        is not part of any reference appears in the input stream.
187        The document is non‐conforming.</p>
188    
189        <p><em>Any <code>&amp;</code> character in URI (or IRI)
190        must be escaped as <code class="example">&amp;amp;</code>.</em></p>
191    
192        <p>The <code>&amp;</code> character must
193        be the first character of a reference:
194          <dl class="switch">
195          <dt>Named entity reference</dt>
196              <dd><pre class="html example">
197    <code>&amp;<var>entity-name</var>;</code></pre>
198              where <var>entity-name</var> is the name of the
199              character entity to be referenced.</dd>
200          <dt>Numeric character reference</dt>
201              <dd><pre class="html example">
202    <code>&amp;#<var>d</var>;</code></pre>
203              where <var>d</var> is the decimal representation of
204              the code position of the character to be referenced.</dd>
205          <dt>Hexadecimal character reference</dt>
206              <dd><pre class="html example">
207    <code>&amp;#x<var>h</var>;</code></pre>
208              where <var>h</var> is the hexadecimal representation
209              of the code position of the character to be referenced.</dd>
210          </dl>
211        </p>
212    
213        <p>To represent <code>&amp;</code> as a data character, use
214        named entity reference:
215          <pre class="html example">
216    <code>&amp;amp;</code></pre>
217        </p>
218      </div>
219    
220    <div class="section tokenize-error" id="bare-etago"><h3>A <code>&lt;/</code> string is not followed
221      by a tag name.</h3>
222        <p>There is a <code>&lt;</code> (<code>U+003C</code>
223        <code class="charname">LESS-THAN SIGN</code>) character
224        immediately followed by a <code>/</code> (<code>U+005F</code>
225        <code>SOLIDUS</code>) character, which is not part
226        of any end tag, in the input stream.  The document
227        is non-conforming.</p>
228    
229        <p>The <code>&lt;/</code> sequence immediately followed
230        by an <abbr title="End of file pseudo-character">EOF</abbr> is
231        interpreted as a string data of <code>&lt;/</code>.</p>
232    
233        <p>The <code>&lt;/</code> sequence as string data must
234        be escaped as:
235        <pre class="html example">
236    <code>&amp;lt;/</code></pre>
237        </p>
238      </div>
239    
240    <div class="section tokenize-error" id="bare-stago"><h3>A <code>&lt;</code> character is not followed
241      by tag name or by a <code>!</code> character.</h3>
242        <p>A <code>&lt;</code> (<code>U+003C</code>
243        <code class="charname">LESS-THAN SIGN</code>) character which is not part
244        of any markup appears in the input stream.</p>
245    
246        <p>The <code>&lt;</code> character as a data character must
247        be escaped as:
248        <pre class="html example">
249    <code>&amp;lt;</code></pre>
250        </p>
251      </div>
252    
253    <div class="section tokenize-error" id="bare-nero"><h3>The decimal representation of the code position
254      of a character must be specified after <code>&amp;#</code>.</h3>
255        <p>An <code>&amp;</code> (<code>U+0026</code>
256        <code class="charname">AMPERSAND</code>) character immediately
257        followed by a <code>#</code> (<code>U+0023</code>
258        <code>NUMBER SIGN</code>) character which
259        is not part of any reference appears in the input stream.
260      The document is non-conforming.</p>      The document is non-conforming.</p>
261    
262        <p>The string <code>&amp;#</code> must be the first two characters
263        of a reference:
264          <dl class="switch">
265          <dt>Numeric character reference</dt>
266              <dd><pre class="html example">
267    <code>&amp;#<var>d</var>;</code></pre>
268              where <var>d</var> is the decimal representation of
269              the code point of the character to be referenced.</dd>
270          <dt>Hexadecimal character reference</dt>
271              <dd><pre class="html example">
272    <code>&amp;#x<var>h</var>;</code></pre>
273              where <var>h</var> is the hexadecimal representation
274              of the code point of the character to be referenced.</dd>
275          </dl>
276        </p>
277    
278        <p>To represent <code>&amp;#</code> as data characters, use
279        a named entity reference for the <code>&amp;</code> character:
280          <pre class="html example">
281    <code>&amp;amp;#</code></pre>
282        </p>
283      </div>
284    
285    <div class="section tokenize-error" id="bare-hcro"><h3>The hexadecimal representation of the code position
286      of a character must be specified after <code>&amp;#x</code>.</h3>
287       <p>The string <code>&amp;#x</code> or <code>&amp;#X</code> which
288       is not part of any reference appears in the input stream.
289        The document is non-conforming.</p>
290    
291        <p>The string <code>&amp;#x</code> or <code>&amp;#X</code> must
292        be the first three characters of a hexadecimal reference:
293          <pre class="html example">
294    <code>&amp;#x<var>h</var>;</code></pre>
295        where <var>h</var> is the hexadecimal representation
296        of the code point of the character to be referenced.</p>
297    
298        <p>To represent <code>&amp;#x</code> as data characters, use
299        a named entity reference for the <code>&amp;</code> character:
300          <pre class="html example">
301    <code>&amp;amp;#x</code></pre>
302        </p>
303      </div>
304    
305    <div class="section tokenize-error" id="bogus-comment"><h3>String <code>&lt;!</code> is not followed
306      by <code>--</code>.</h3>
307        <p>There is a <code>&lt;</code> (<code>U+003C</code>
308        <code class="charname">LESS-THAN SIGN</code>) character
309        followed by a <code>!</code> (<code>U+0021</code>
310        <code class="charname">EXCLAMATION MARK</code>) character,
311        which is not followed by a <code>--</code> or
312        <code>!DOCTYPE</code>.  The document is non-conforming.</p>
313    
314        <dl class="switch">
315        <dt>Comments</dt>
316          <dd>In HTML document, comments must be introduced by
317          <code class="example">&lt;!--</code> (<code>&lt;!</code>
318          <em>immediately</em> followed
319          by <em>two</em> <code>-</code>s) and must be terminated by
320          <code class="example">--&gt;</code>.
321          Strings <code>&lt;!</code> not followed
322          by <code>--</code> and <code>&lt;!-</code> not followed by
323          <code>-</code> are not valid open delimiters for comments.</dd>
324        <dt>Marked sections, including <code>CDATA</code> sections</dt>
325          <dd>Marked sections are not allowed in HTML document.</dd>
326        <dt>Markup declarations</dt>
327          <dd>Markup declarations, except for <code>DOCTYPE</code>
328          and comment declarations, are not allowed in HTML document.</dd>
329        <dt>String <code>&lt;!</code></dt>
330          <dd>String <code>&lt;!</code> must be escaped as
331          <code class="example">&amp;lt;!</code>.</dd>
332        </dl>
333    </div>    </div>
334    
335  <div class="section tokenize-error" id="duplicate-attribute"><h3>There are two attributes with same name.</h3>  <div class="section tokenize-error" id="bogus-end-tag"><h3>String <code>&lt;/</code> is not followed
336      <p>Attributes must be unique in an element.  Specifying    by tag name.</h3>
337      attributes with same name more than once is non-conforming.</p>      <p>There is a <code>&lt;</code> (<code>U+003C</code>
338        <code class="charname">LESS-THAN SIGN</code>) character
339        immediately followed by a <code>/</code> (<code>U+005F</code>
340        <code>SOLIDUS</code>) character, which is not part
341        of any end tag, in the input stream.  The document
342        is non-conforming.</p>
343    
344        <p>The <code>&lt;/</code> sequence not followed by a
345        tag name is parsed as an opening of bogus comment.</p>
346    
347        <p>The <code>&lt;/</code> sequence as string data must
348        be escaped as:
349        <pre class="html example">
350    <code>&amp;lt;/</code></pre>
351        </p>
352      </div>
353    
354    <div class="section tokenize-error" id="C1-character-reference"><h3>Character reference to
355      <code><var>{text}</var></code> is not allowed.</h3></div>
356    
357    <div class="section tokenize-error" id="CR-character-reference"><h3>Character reference to
358      <code>U+000D</code> (<code class="charname">CARRIAGE RETURN</code>)
359      is not allowed.</h3></div>
360    
361    <div class="section tokenize-error" id="dash-in-comment"><h3>There is a <code>--</code> sequence
362      in a comment.</h3>
363        <p>There is a <code>-</code> (<code>U+002D</code>
364        <code class="charname">HYPHEN-MINUS</code>) character
365        at the end of the comment or a <code>--</code> sequence
366        in the comment.  The document is non-conforming.</p>
367    
368        <p>Comments cannot contain a string <code>--</code>, as in XML.
369        Unlike SGML, there cannot be more than one comments
370        (where <i>comment</i> is an SGML term) in the comment
371        declaration.</p>
372      </div>
373    
374    <div class="section tokenize-error" id="duplicate-attribute"><h3>There are two attributes with name
375          <code><var>{text}</var></code>.</h3>
376        <p>There are more than one attributes with the same
377        name in a tag.  The document is non-conforming.</p>
378    
379      <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.
380      Use <code>img</code> element with animation GIF instead.</p>      Use <code>img</code> element with animation GIF instead.</p>
381    </div>    </div>
382    
383  <div class="section tokenize-error" id="nestc"><h3>Void element syntax (<code>/&gt;</code>) cannot be  <div class="section tokenize-error" id="empty-start-tag"><h3>Empty start tag (<code>&lt;&gt;</code>) is not
384      allowed.</h3></div>
385    
386    <div class="section tokenize-error" id="empty-end-tag"><h3>Empty end tag (<code>&lt;/&gt;</code>) is not
387      allowed.</h3></div>
388    
389    <div class="section tokenize-error" id="end-tag-attribute"><h3>End tag cannot have attributes.</h3></div>
390    
391    <div class="section tokenize-error" id="invalid-character-reference"><h3>Character reference to
392      <code><var>{text}</var></code> is not allowed.</h3></div>
393    
394    <div class="section tokenize-error" id="nestc"><h3>Polytheistic slash (<code>/&gt;</code>) cannot be
395    used for this element.</h3>    used for this element.</h3>
396      <p>The void element syntax <code>/&gt;</code> syntax can only be      <p>Polytheistic slash (<code>/&gt;</code>) must not be used
397        for the element.  The document is non-conforming.</p>
398    
399        <p>The polytheistic slash can only be
400      used for <code>base</code>, <code>link</code>, <code>meta</code>,      used for <code>base</code>, <code>link</code>, <code>meta</code>,
401      <code>hr</code>, <code>br</code>, <code>img</code>,      <code>hr</code>, <code>br</code>, <code>img</code>,
402      <code>embed</code>, <code>param</code>, <code>area</code>,      <code>embed</code>, <code>param</code>, <code>area</code>,
403      <code>col</code>, and <code>input</code> elements.      <code>col</code>, and <code>input</code> elements.</p>
404      For any other elements, using that syntax is non-conforming.</p>  
405        <dl class="switch">
406        <dt><code>&lt;script/&gt;</code></dt>
407            <dd><p>The polytheistic slash cannot be used for <code>script</code>
408            element.  Even for an empty <code>script</code> element,
409            there must be an explicit end tag
410            <code class="html example">&lt;/script&gt;</code>.</p>
411    
412            <p><strong>NOTE</strong>: Though some user agents interpret
413            polytheistic slash for <code>script</code> element as the
414            closing of the element, such usage is not allowed under
415            the current standard.</p></dd>
416        <dt><code>&lt;basefont/&gt;</code>, <code>&lt;bgsound/&gt;</code>,
417        <code>&lt;frame/&gt;</code>, <code>&lt;keygen/&gt;</code>,
418        <code>&lt;spacer/&gt;</code>, <code>&lt;wbr/&gt;</code></dt>
419            <dd>These elements are themselves non-conforming.</dd>
420        <!-- isindex, image -->
421        <dt><code>&lt;command/&gt;</code>, <code>&lt;event-source/&gt;</code>,
422        <code>&lt;nest/&gt;</code>, or <code>&lt;source/&gt;</code></dt>
423            <dd>Future revision of HTML5 parsing algorithm is expected
424            to allow polytheistic slash for these elements.</dd>
425        <dt><code>&lt;a/&gt;</code>, <code>&lt;p/&gt;</code></dt>
426            <dd>These elements are not always empty and therefore
427            polytheistic slash is not allowed.  Use explicit end tag
428            to represent empty element as:
429              <pre class="example html">
430    <code>&lt;p&gt;&lt;/p&gt;</code></pre>
431            </dd>
432        </dl>
433    
434      <p>Unlike XML, the void element syntax (<code>/&gt;</code>) has      <p>Note that, unlike in XML, the polytheistic slash has
435      no effect in HTML.</p>      no effect in HTML.</p>
436    </div>    </div>
437    
438    <div class="section tokenize-error" id="no-DOCTYPE-name"><h3>After the string <code>&lt;!DOCTYPE </code>, the
439      document type name must be specified.</h3></div>
440    
441    <div class="section tokenize-error" id="no-PUBLIC-literal"><h3>After the keyword <code>PUBLIC</code>, no
442      oublic identifier is specified.</h3></div>
443    
444    <div class="section tokenize-error" id="no-refc"><h3>Character reference must be closed by a
445      <code>;</code> character.</h3></div>
446    
447    <div class="section tokenize-error" id="no-space-before-DOCTYPE-name"><h3>After the string <code>&lt;!DOCTYPE</code>, there
448      must be at least a white space character before the document type
449      name.</h3></div>
450    
451    <div class="section tokenize-error" id="no-space-between-attributes"><h3>Attributes must be separeted by at least a
452      white space character.</h3></div>
453    
454    <div class="section tokenize-error" id="no-SYSTEM-literal"><h3>After the keyword <code>SYSTEM</code>, no
455      system identifier is specified.</h3></div>
456    
457    <div class="section tokenize-error" id="pio"><h3>Processing instruction
458      (<code>&lt;?<var>...</var>&gt;</code>) is not allowed in HTML
459      document.</h3>
460        <p>Processing instructions (<code>&lt;?<var>...</var>?&gt;</code>),
461        including XML declaration (<code>&lt;?xml <var>...</var>?&gt;</code>)
462        and XML style sheet <abbr title="processing instruction">PI</abbr>
463        (<code>&lt;?xml-stylesheet <var>...</var>?&gt;</code>), are not allowed
464        in the HTML syntax.  The document is non-conforming.</p>
465    
466        <dl class="switch">
467        <dt><code>&lt;?xbl?&gt;</code> (<abbr>XBL</abbr> Association)</dt>
468          <dd>An <abbr>XBL</abbr> binding cannot be associated by
469          <abbr title="processing instruction">PI</abbr> in <abbr>HTML</abbr>
470          document.  Use <code>binding</code> property in <abbr>CSS</abbr>
471          style sheet as:
472            <pre class="html example">
473    <code>&lt;style&gt;
474    p {
475      binding: url(binding.xbl);
476    }
477    &lt;/style&gt;</code></pre>
478          </dd>
479        <dt><code>&lt;?xml?&gt;</code> (XML declaration)</dt>
480            <dd>XML declaration is unnecessary for HTML documents.</dd>
481        <dt><code>&lt;?xml-stylesheet?&gt;</code> (XML style sheet
482        <abbr title="processing instruction">PI</abbr>)</dt>
483            <dd>Use HTML <code>link</code> element with <code>rel</code>
484            attribute set to <code>stylesheet</code> (or,
485            <code>alternate stylesheet</code> for an alternate style
486            sheet).
487              <pre class="example html">
488    <code>&lt;link rel=stylesheet href="path/to/stylesheet.css"&gt;</code></pre>
489            </dd>
490        <dt><code>&lt;?php?&gt;</code> or
491        <code>&lt;? <var>... <abbr>PHP</abbr> code ...</var> ?&gt;</code>
492        (<abbr>PHP</abbr> code)</dt>
493            <dd>The conformance checker does <em>not</em> support
494            checking for PHP source documents.</dd>
495        <dt>Other processing instructions</dt>
496            <dd>Processing instructions cannot be inserted in an HTML
497            document.  Use XML document or insert
498            <code>ProcessingInstruction</code> node by scripting.</dd>
499        </dl>
500    
501        <p>Web browsers will parse processing instructions as bogus
502        comments.  Some legacy Web browsers, such as IE:mac and
503        some mobile Web browsers, will display processing instructions
504        as string.</p>
505      </div>
506    
507    <div class="section tokenize-error" id="string-after-DOCTYPE-name"><h3>There is a bogus string after the document type
508      name.</h3></div>
509    
510    <div class="section tokenize-error" id="string-after-PUBLIC"><h3>There is a bogus string after the keyword
511      <code>PUBLIC</code>.</h3></div>
512    
513    <div class="section tokenize-error" id="string-after-PUBLIC-literal"><h3>There is a bogus string after the public
514      identifier.</h3></div>
515    
516    <div class="section tokenize-error" id="string-after-SYSTEM"><h3>There is a bogus string after the keyword
517      <code>SYSTEM</code>.</h3></div>
518    
519    <div class="section tokenize-error" id="string-after-SYSTEM-literal"><h3>There is a bogus string after the system
520      identifier.</h3></div>
521    
522    <div class="section tokenize-error" id="unclosed-attribute-value"><h3>Attribute value is not closed by a quotation
523      mark.</h3></div>
524    
525    <div class="section tokenize-error" id="unclosed-comment"><h3>Comment is not closed by a string
526      <code>--&gt;</code>.</h3></div>
527    
528    <div class="section tokenize-error" id="unclosed-DOCTYPE"><h3>The <code>DOCTYPE</code> is not closed by a
529      <code>&gt;</code> character.</h3></div>
530    
531    <div class="section tokenize-error" id="unclosed-PUBLIC-literal"><h3>The public identifier literal is not closed by a
532      quotation mark.</h3></div>
533    
534    <div class="section tokenize-error" id="unclosed-SYSTEM-literal"><h3>The system identifier literal is not closed by a
535      quotation mark.</h3></div>
536    
537    <div class="section tokenize-error" id="unclosed-tag"><h3>Tag is not closed by a <code>&gt;</code>
538      character.</h3></div>
539    
540    </section>
541    
542    <section id="html5-parse-errors">
543    <h2>HTML5 Parse Errors in Tree Construction Stage</h2>
544    
545    <div class="section parse-error" id="after-body"><h3>Start tag <code>&lt;<var>{text}</var>&gt;</code> is
546      not allowed after the <code>body</code> is closed.</h3></div>
547    
548    <div class="section parse-error" id="after-body:/"><h3>End tag <code>&lt;/<var>{text}</var>&gt;</code> is
549      not allowed after the <code>body</code> is closed.</h3></div>
550    
551    <div class="section parse-error" id="after-body:#text"><h3>Non‐white‐space characters are not allowed
552      after the <code>body</code> is closed.</h3></div>
553    
554    <div class="section parse-error" id="after-frameset"><h3>Start tag <code>&lt;<var>{text}</var>&gt;</code> is
555      not allowed after the <code>frameset</code> is closed.</h3></div>
556    
557    <div class="section parse-error" id="after-frameset:/"><h3>End tag <code>&lt;/<var>{text}</var>&gt;</code> is
558      not allowed after the <code>frameset</code> is closed.</h3></div>
559    
560    <div class="section parse-error" id="after-frameset:#text"><h3>Non‐white‐space characters are not allowed
561      after the <code>frame</code> is closed.</h3></div>
562    
563    <div class="section parse-error" id="after-head"><h3>The <code><var>{text}</var></code> element cannot be
564      inserted between <code>head</code> and <code>body</code>
565      elements.</h3>
566        <p>A start tag appears after the <code>head</code> element is closed
567        but before the <code>body</code> element is opened.
568        The document is non-conforming.</p>
569      </div>
570    
571    <div class="section parse-error" id="after-html"><h3>Start tag <code>&lt;<var>{text}</var>&gt;</code> is
572      not allowed after the <code>html</code> is closed.</h3></div>
573    
574    <div class="section parse-error" id="after-html:/"><h3>End tag <code>&lt;/<var>{text}</var>&gt;</code> is
575      not allowed after the <code>html</code> is closed.</h3></div>
576    
577    <div class="section parse-error" id="after-html:#text"><h3>Non‐white‐space characters are not allowed
578      after the <code>html</code> is closed.</h3></div>
579    
580    <div class="section parse-error" id="image"><h3>The <code>image</code> element is
581      obsolete.</h3></div>
582    
583    <div class="section parse-error" id="in-a:a"><h3>Anchor cannot be nested.</h3>
584        <p>HTML <code>a</code> elements cannot be nested.
585        The document is non-conforming.</p>
586    
587        <p>In the HTML syntax, a start tag of the <code>a</code>
588        implies the end tag of any opening <code>a</code> element.</p>
589      </div>
590    
591    <div class="section parse-error" id="in-body"><h3>Start tag <code>&lt;<var>{text}</var>&gt;</code>
592      is not allowed in the <code>body</code> element.</h3>
593        <p>The start or end tag of an element, which
594        cannot be a descendant of <code>body</code> element, appears
595        in the input stream while the <code>body</code> element has been opened.
596        The document is non-conforming.</p>
597      </div>
598    
599    <div class="section parse-error" id="in-body:#eof"><h3>Some element is not closed before the end of
600      file.</h3></div>
601    
602    <div class="section parse-error" id="in-button:button"><h3>The <code>button</code> element cannot be
603      nested.</h3></div>
604    
605    <div class="section parse-error" id="in-CDATA:#eof"><h3>Element is not closed before the end of
606      file.</h3></div>
607    
608    <div class="section parse-error" id="in-form:form"><h3>Start tag <code>&lt;form&gt;</code> is
609      not allowed in a <code>form</code> element.</h3></div>
610    
611    <div class="section parse-error" id="in-frameset"><h3>Start tag <code>&lt;<var>{text}</var>&gt;</code> is
612      not allowed in a <code>framset</code> element.</h3></div>
613    
614    <div class="section parse-error" id="in-frameset:/"><h3>End tag <code>&lt;/<var>{text}</var>&gt;</code> is
615      not allowed in a <code>frameset</code> element.</h3></div>
616    
617    <div class="section parse-error" id="in-frameset:#text"><h3>Non‐white‐space characters are not allowed
618      in a <code>frameset</code> element.</h3></div>
619    
620    <div class="section parse-error" id="in-head:head"><h3>Start tag <code>&lt;head&gt;</code>
621      is not allowed in the <code>head</code> element.</h3>
622        <p>There is a start tag <code>&lt;head&gt;</code> in the
623        <code>&lt;head&gt;</code> element.  The document is non-conforming.</p>
624    
625        <p>In an HTML document there must not be more than
626        one <code>head</code> element, therefore no more than one
627        start tag <code>&lt;head&gt;</code> can appear in the input stream.</p>
628      </div>
629    
630    <div class="section parse-error" id="in-html:#DOCTYPE"><h3>A <code>DOCTYPE</code> appears after any
631      element or data character has been seen.</h3>
632        <p>A <code>DOCTYPE</code> appears after any element or data character
633        has been seen.  The document is non-conforming.</p>
634        
635        <p>The <code>DOCTYPE</code> must be placed before any
636        tag, reference, or data character.  Only white space characters
637        and comments can be inserted before the <code>DOCTYPE</code>.</p>
638      </div>
639    
640    <div class="section parse-error" id="in-nobr:nobr"><h3>The <code>nobr</code> element cannot be
641      nested.</h3></div>
642    
643    <div class="section parse-error" id="in-noscript"><h3>The <code><var>{text}</var></code> element is not
644      allowed in a <code>noscript</code> element in the
645      <code>head</code> element.</h3></div>
646    
647    <div class="section parse-error" id="in-noscript:/"><h3>An end tag <code>&lt;/<var>{text}</var>&gt;</code>
648      appers before the <code>noscript</code> element is closed.</h3></div>
649    
650    <div class="section parse-error" id="in-noscript:#eof"><h3>A <code>noscript</code> element is not closed
651      before the end of file.</h3></div>
652    
653    <div class="section parse-error" id="in-noscript:#text"><h3>Non‐white‐space characters are not allowed
654      in a <code>noscript</code> element in the <code>head</code>
655      element.</h3></div>
656    
657    <div class="section parse-error" id="in-PCDATA:#eof"><h3>Element is not closed before the end of
658      file.</h3></div>
659    
660    <div class="section parse-error" id="in-select"><h3>Start tag <code>&lt;<var>{text}</var>&gt;</code>
661      is not allowed in a <code>select</code> element.</h3></div>
662    
663    <div class="section parse-error" id="in-select:/"><h3>End tag <code>&lt;/<var>{text}</var>&gt;</code>
664      is not allowed in a <code>select</code> element.</h3></div>
665    
666    <div class="section parse-error" id="in-table"><h3>Start tag <code>&lt;<var>{text}</var>&gt;</code>
667      is not allowed in a <code>table</code> element.</h3>
668        <p>The start or end tag of an element, which
669        cannot be a child of <code>table</code> element, appears
670        in the input stream while the <code>table</code> element has been opened
671        but no other element has been opened.  The document is non-conforming.</p>
672    
673        <p>In <code>table</code>, only table related elements
674        are allowed; any other element must be contained in
675        <code>td</code> or <code>th</code> element to form
676        a part of the table, or <code>caption</code> element to create
677        a table caption.</p>
678      </div>
679    
680    <div class="section parse-error" id="in-table:/"><h3>End tag <code>&lt;/<var>{text}</var>&gt;</code>
681      is not allowed in a <code>table</code> element.</h3></div>
682    
683    <div class="section parse-error" id="in-table:#text"><h3>Non‐white‐space character is not allowed within
684      the <code>table</code> element, outside of the caption and cells.</h3>
685        <p>A non‐white‐space character appears in <code>table</code>.
686        The document is non-conforming.</p>
687    
688        <p>In <code>table</code>, only table related elements
689        are allowed; any other element and data character must be contained in
690        <code>td</code> or <code>th</code> element to form
691        a part of the table, or <code>caption</code> element to create
692        a table caption.</p>
693      </div>
694    
695    <div class="section parse-error" id="isindex"><h3>The <code>isindex</code> element is
696      obsolete.</h3></div>
697    
698    <div class="section parse-error" id="missing-start-tag:tr"><h3>Start tag of <code>tr</code>
699      element is missing.</h3>
700        <p>Start tag of a <code>tr</code> element, which is <em>not</em>
701        optional, is missing.  The document is non-conforming.</p>
702    
703        <p>In a table section, a <code>&lt;tr&gt;</code> start tag
704        must occur before any <code>&lt;td&gt;</code> or
705        <code>&lt;th&gt;</code> start tag.  Though the HTML5 parser
706        implies the <code>&lt;tr&gt;</code> start tag before
707        these start tags, it must be explicitly specified.</p>
708      </div>
709    
710    <div class="section parse-error" id="no-DOCTYPE"><h3>This document does not start with a
711      <code>DOCTYPE</code>.</h3>
712        <p>The document does not start with a <code>DOCTYPE</code>.
713        The document is non-conforming.</p>
714    
715        <p>An HTML document must start by a <code>DOCTYPE</code>:
716          <pre class="html example">
717    <code>&lt;!DOCTYPE HTML&gt;</code></pre>
718        </p>
719    
720        <p>Only white space characters and comments are allowed
721        before the <code>DOCTYPE</code>.  XML declaration is <em>not</em>
722        allowed in HTML document.</p>
723      </div>
724    
725    <div class="section parse-error" id="not-closed"><h3>Element <code><var>{text}</var></code> is not
726      closed.</h3>
727        <p>End tag of an element is not found before, for example,
728        an end tag of another element appears or
729        the end of the document.  The document is non-conforming.</p>
730    
731        <p>Only <code>body</code>, <code>colgroup</code>, <code>dd</code>,
732        <code>dt</code>, <code>head</code>, <code>html</code>, <code>li</code>,
733        <code>ol</code>, <code>option</code>, <code>optgroup</code>,
734        <code>p</code>, <code>rb</code>, <code>rp</code>, <code>rt</code>,
735        <code>tbody</code>, <code>td</code>, <code>tfoot</code>,
736        <code>th</code>, <code>thead</code>, <code>tr</code>,
737        <code>ul</code> end tag can be omitted in HTML documents.
738        For any element except for void element, there must be an explicit
739        end tag.</p>
740    
741        <dl class="switch">
742        <dt>HTML <code>canvas</code> element</dt>
743          <dd>Though the element is void in earlier versions of Safari,
744          the <code>canvas</code> element is <em>no</em> longer
745          defined as empty.  There must be an end tag
746          <code class="html example">&lt;/canvas&gt;</code>.</dd>
747        </dl>
748    
749        <p>Note that misnesting tags, such as
750        <code class="bad example">&lt;a&gt;&lt;b&gt;&lt;/a&gt;&lt;/b&gt;</code>, are not
751        allowed and they also cause this error.</p>
752      </div>
753    
754    <div class="section parse-error" id="not-first-start-tag"><h3>This <code>&lt;html&gt;</code> tag is not
755      the first start tag.</h3>
756        <p>There is a start tag of the <code>html</code> element
757        that it not the first start tag in the input stream.
758        The document is non-conforming.</p>
759    
760        <p>In an HTML document, there cannot be more than one
761        <code>html</code> element and therefore there cannot be
762        more than one <code>&lt;html&gt;</code> tag.  In addition,
763        nothing can be placed before the <code>&lt;html&gt;</code> tag
764        except a <code>DOCTYPE</code>, white space characters,
765        and comments.</p>
766      </div>
767    
768    <div class="section parse-error" id="not-HTML5"><h3>This document is written in an old version of
769      HTML.</h3>
770        <p>The document contains a <code>DOCTYPE</code> declaration
771        that is different from HTML5 <code>DOCTYPE</code> (i.e.
772        <code class="example html">&lt;!DOCTYPE HTML&gt;</code>).
773        The document is non‐conforming.</p>
774    
775        <p>The document might or might not be conformant to
776        some version of HTML.  However, conformance to any HTML
777        specification other than HTML5 provides for no practical
778        convenience, since Web borwsers will parse any
779        HTML document (roughly) as defined in HTML5.</p>
780      </div>
781    
782    <div class="section parse-error" id="start-tag-not-allowed"><h3>Start tag <code>&lt;<var>{text}</var>&gt;</code> is
783      not allowed here.</h3></div>
784    
785    <div class="section parse-error" id="unmatched-end-tag"><h3>Element <code><var>{text}</var></code> is not
786      opened.</h3>
787        <p>An end tag appears though no element with the same name
788        has been opened.  The document is non-conforming.</p>
789    
790        <p>For any end tag in HTML document, there must be a
791        corresponding start tag.</p>
792    
793        <dl class="switch">
794        <dt>HTML <code>base</code>, <code>basefont</code>,
795        <code>bgsound</code>, <code>br</code>, <code>col</code>,
796        <code>embed</code>, <code>frame</code>, <code>hr</code>,
797        <code>image</code>, <code>img</code>, <code>input</code>,
798        <code>isindex</code>, <code>link</code>, <code>meta</code>,
799        <code>param</code>, <code>spacer</code>, or <code>wbr</code> element</dt>
800          <dd>End tag is not allowed for these elements, since
801          those content must always be empty.  Remove end tag.</dd>
802        <!-- keygen -->
803        <!-- command, event-source, nest, source -->
804        </dl>
805      </div>
806    
807  </section>  </section>
808    
809  <section id="element-content-model-errors">  <section id="element-content-model-errors">
810  <h2>Element Content Model Errors</h2>  <h2>Element Content Model Errors</h2>
811    
812  <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
813      <code>href</code> attribute specified cannot be placed after
814      any attribute with a URL.</h3></div>
815    
816    <div class="section " id="basetarget-after-hyperlink"><h3>The <code>base</code> element with the
817      <code>target</code> attribute specified cannot be placed after
818      any element that defines a hyperlink.</h3></div>
819    
820    <div class="section " id="character-not-allowed"><h3>Data character is not allowed in this
821    context.</h3>    context.</h3>
822      <p>A data character occurs where it is not allowed in this      <p>A data character appears where it is not allowed in this
823      context.  The document is non-conforming.</p>      context.  The document is non-conforming.</p>
824    
825      <p>Possible causes:      <p>Possible causes:
826        <dl>        <ul>
827        <dt>If the erred element is an inline-level element (such        <li><p>A data character cannot be a child
828        as <code>a</code> or <code>span</code>)</dt>        of certain sectioning elements such as <code>body</code>,
829            <dd><p>A data character cannot be a child        <code>section</code>, and <code>blockquote</code>.</p>
830            of certain sectioning elements such as <code>body</code>,  
831            <code>section</code>, and <code>blockquote</code>.</p>        <p>Any inline-level content must be put
832          in e.g. paragraph element such as <code>p</code>.</p></li>
833            <p>Any inline-level content must be put        <li><p>Though some elements such as <code>div</code>,
834            in e.g. paragraph element such as <code>p</code>.</p></dd>        <code>li</code>, and <code>td</code> allow
835        <dt>If the erred element is a block-level element (such as        <em>either one</em> of block-level or inline-level content
836        <code>div</code> or <code>h<var>n</var></code>)</dt>        is allowed.  If there is a block-level content,
837            <dd><p>Though some elements such as <code>div</code>,        any inline-level content must be put
838            <code>li</code>, and <code>td</code> allow        in e.g. paragraph element such as <code>p</code>.</p></li>
839            <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>  
840      </p>      </p>
841    </div>    </div>
842    
843  <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
844    element as a child of this element.</h3>    an empty element.</h3></div>
845    
846    <div class="section " id="character-not-allowed:atom|PersonConstruct"><h3>Non‐white‐space characters are not allowed in
847      Person construct.</h3></div>
848    
849    <div class="section " id="character-not-allowed:atom|TextConstruct"><h3>Non‐white‐space characters are not allowed in
850      Text construct.</h3></div>
851    
852    <div class="section " id="child-element-missing"><h3>There must be an element
853      <code><var>{text}</var></code> as a child of this element.</h3>
854      <p>The content model of the element is so defined that it      <p>The content model of the element is so defined that it
855      must contain a <code><var>$0</var></code> child element.      must contain a <code><var>$0</var></code> child element.
856      Without such an element, the document is non-conforming.</p>      The document is non-conforming.</p>
857    
858      <p>For example:      <dl class="switch">
859        <ul>      <dt>HTML <code>head</code> element</dt>
860        <li>The <code>head</code> element must contain exactly one        <dd>There must be a <code>title</code> child element.</dd>
861        <code>title</code> child element.</li>      <dt>HTML <code>html</code> element</dt>
862        <li><a href="#child-element-missing:td%7Cth">The <code>tr</code>        <dd>There must be a <code>head</code> child element followed
863        element must contain one or more <code>td</code> or <code>th</code>        by a <code>body</code> element.</dd>
864        child element.</a></li>      <dt>HTML <code>tr</code> element</dt>
865        </ul>        <dd><a href="#child-element-missing:td%7Cth">There must be
866      </p>        one or more <code>td</code> or <code>th</code> child element.</a></dd>
867        </dl>
868    </div>    </div>
869    
870  <div class="section content-model-error" id="child-element-missing:td|th"><h3>There must be a <code>td</code>  <div class="section content-model-error" id="child-element-missing:td|th"><h3>There must be a <code>td</code>
871    or <code>th</code> element as a child of this element.</h3>    or <code>th</code> element as a child of this element.</h3>
872      <p>The <code>tr</code> element must contain at least one      <p>The <code>tr</code> element must contain at least one
873      <code>td</code> or <code>th</code> child element.  Without      <code>td</code> or <code>th</code> child element.  The document
874      such an element, the document is non-conforming.</p>      is non-conforming.</p>
875    </div>    </div>
876    
877  <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
878      <code><var>{text}</var></code> in the Atom namespace as a child of this
879      element.</h3></div>
880    
881    <div class="section " id="child-element-missing:atom:link:alternate"><h3>There must be an Atom <code>link</code> element
882      whose <code>rel</code> attribute is set to <code>alternate</code> as a
883      child of this element.</h3></div>
884    
885    <div class="section " id="child-element-missing:atom:link:self"><h3>There should be an Atom <code>link</code> element
886      whose <code>rel</code> attribute is set to <code>self</code> as a
887      child of this element.</h3></div>
888    
889    <div class="section " id="element-missing:hn"><h3>There must be at least one
890      <code>h<var>n</var></code> element descendant.</h3></div>
891    
892    <div class="section " id="element-not-allowed"><h3>This element is not allowed in this
893    context.</h3>    context.</h3>
894      <p>An element occurs where it is not allowed.  The document      <p>An element appears where it is not allowed.  The document
895      is non-conforming.</p>      is non-conforming.</p>
896    
897      <p>Possible causes:      <p>Possible causes:
898        <dl>        <dl class="switch">
899        <dt>If the erred element is an inline-level element (such        <dt>If the element with the error is an inline-level element,
900        as <code>a</code> or <code>span</code>)</dt>        such as <code>a</code>, <code>progress</code>, or <code>img</code></dt>
901            <dd><p>An inline-level element cannot be a child            <dd><p>An inline-level element cannot be a child
902            of certain sectioning elements such as <code>body</code>,            of certain sectioning elements such as <code>body</code>,
903            <code>section</code>, and <code>blockquote</code>.</p>            <code>section</code>, and <code>blockquote</code>.</p>
904    
905            <p>Any inline-level content must be put            <p>Any inline-level content must be put
906            in e.g. paragraph element such as <code>p</code>.</p></dd>            in e.g. paragraph element such as <code>p</code>.</p></dd>
907        <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>,
908        <code>div</code> or <code>h<var>n</var></code>)</dt>        <code>div</code>, <code>h<var>n</var></code>,
909            <dd><p>Though some elements such as <code>div</code>,        <code>p</code>, or <code>section</code></dt>
910            <code>li</code>, and <code>td</code> allow            <dd><dl class="switch">
911            <em>either one</em> of block-level or inline-level content                <dt>If the parent element is <code>div</code>,
912            is allowed.  If there is a block-level content,                <code>li</code>, <code>td</code>, or <code>th</code></dt>
913            any inline-level content must be put                <!-- @@ TODO: more... -->
914            in e.g. paragraph element such as <code>p</code>.</p></dd>                    <!-- @@ TODO: <p><ul><li><p> -->
915        <dt>If the erred element is the root <code>html</code> element</dt>                    <dd><p>The parent element allows <em>either</em>
916            <dd><p>In an XHTML document, the root <code>html</code>                    block-level or inline-level content.  If there is a
917            element must have an <code>xmlns</code> attribute                    block-level content, any inline-level content must be
918            whose value is set to                    put in e.g. paragraph element such as <code>p</code>.</p>
919            <code>http://www.w3.org/1999/xhtml</code>.</p></dd>                    <p>For example, an HTML document fragment
920                      <code class="html bad example">&lt;div&gt;&lt;p&gt;Hello!&lt;/p&gt; World!&lt;/div&gt;</code>
921                      is non-conforming, since a word <q>World!</q> does not belong
922                      to any paragraph.  (If not part of any paragraph, what is
923                      it!?)  A conforming example would be:
924                        <pre class="html example">
925    <code>&lt;div&gt;&lt;p&gt;Hello!&lt;/p&gt; &lt;p&gt;World!&lt;/p&gt;&lt;/div&gt;</code></pre>
926                      </p></dd>
927                  <dt>If the parent element does <em>not</em> allow
928                  block-level elements as content</dt>
929                      <dd>The element is not allowed to be inserted here.
930                      For example, a <code>div</code> element cannot be
931                      a child of an <code>h1</code> element.</dd>
932              </dl></dd>
933          <dt>If the element with the error is a <code>noscript</code> element</dt>
934              <dd>The <code>noscript</code> element is allowed only in the context
935              where a block-level or inline-level content is expected
936              and in the <code>head</code> element.
937              It cannot be used in e.g. <code>ul</code>, <code>table</code>,
938              or <code>select</code>.</dd>
939          <dt>If the element with the error is <code>blink</code>,
940          <code>center</code>, or <code>marquee</code> element</dt>
941              <dd>These elements are not part of the HTML standard.
942              Use CSS for styling control.</dd>
943    
944          <dt><code>button</code>, <code>datalist</code>,
945          <code>fieldset</code>, <code>form</code>,
946          <code>input</code>, <code>label</code>,
947          <code>optgroup</code>, <code>option</code>, <code>output</code>,
948          <code>rb</code>, <code>rp</code>, <code>rt</code>, <code>ruby</code>,
949          <code>textarea</code>, or <code>textarea</code> element</dt>
950          <!-- rbc, rtc ? -->
951              <dd>These elements are intentionally not supported by the conformance
952              checker <em>yet</em>.</dd>
953        </dl>        </dl>
954      </p>      </p>
955    </div>    </div>
956    
957  enumerated:invalid;attribute-error;This attribute only allow a limited set of values and the specified value is not one of them.  <div class="section " id="element-not-allowed:area"><h3>An <code>area</code> element cannot be used
958  no DOCTYPE;parse-error;This document does not start with the <code>DOCTYPE</code> declaration.    outside of a <code>map</code> element.</h3></div>
959  not HTML5;parse-error;This document is written in an old version of HTML.  
960  not closed;parse-error;Element <code>$0</code> is not closed.  <div class="section " id="element-not-allowed:base"><h3>There is another <code>base</code>
961  unmatched end tag;parse-error;Element <code>$0</code> is not opened.    element.</h3></div>
962    
963  table:no cell in last row;table-model-error;The table has no cell (<code>td</code> or <code>th</code>) in the last row.  <div class="section " id="element-not-allowed:datatemplate"><h3>In a <code>datatemplate</code> element, only
964      <code>rule</code> elements are allowed.</h3></div>
965  s:IMT:obsolete subtype;should;An <em>obsolete</em> subtype is used.  
966  s:IMT:private subtype;should;A private (<code>x-</code> or <code>x.</code>) subtype is used.  <div class="section " id="element-not-allowed:details-legend"><h3>In a <code>details</code> element, only at the
967  s:IMT:unregistered subtype;should;The subtype is not registered to IANA.    beginning of the element a <code>lengend</code> element
968      may be used.</h3></div>
969    
970    <div class="section " id="element-not-allowed:empty"><h3>Elements are not allowed in an empty
971      element.</h3></div>
972    
973    <div class="section " id="element-not-allowed:figure-legend"><h3>In a <code>figure</code> element, only at the
974      beginning or only at the end of the element a <code>lengend</code> element
975      may be used.</h3></div>
976    
977    <div class="section " id="element-not-allowed:flow"><h3>This element is not allowed where flow
978      content is expected.</h3></div>
979    
980    <div class="section " id="element-not-allowed:flow-style"><h3>A <code>style</code> element without
981      <code>scoped</code> attribute is not allowed in this context.</h3></div>
982    
983    <div class="section " id="element-not-allowed:head-noscript"><h3>This element is not allowed in a
984      <code>noscript</code> element in the <code>head</code> element.</h3></div>
985    
986    <div class="section " id="element-not-allowed:head-style"><h3>A <code>style</code> element with
987      <code>scoped</code> attribute is not allowed in the <code>head</code>
988      element.</h3></div>
989    
990    <div class="section " id="element-not-allowed:head-title"><h3>There is another <code>title</code>
991      element.</h3></div>
992    
993    <div class="section " id="element-not-allowed:minus"><h3>This element is not allowed in this
994      context.</h3></div>
995    
996    <div class="section " id="element-not-allowed:meta-charset"><h3>The character encoding declaration must be the
997      first element in the <code>head</code> element.</h3></div>
998    
999    <div class="section " id="element-not-allowed:metadata"><h3>This element is not allowed where metadata
1000      content is expected.</h3></div>
1001    
1002    <div class="section " id="element-not-allowed:phrasing"><h3>This element is not allowed where phrasing
1003      content is expected.</h3></div>
1004    
1005    <div class="section " id="element-not-allowed:root"><h3>This element is not allowed as the root
1006      element of a document.</h3>
1007        <p>An element that is not allowed as the root element
1008        is used as the root element of the document.  The document is
1009        non-conforming, as far as the conformance checker can tell.</p>
1010    
1011        <dl class="switch">
1012        <dt><code>html</code> element in an XHTML document</dt>
1013            <dd><p>In <abbr>XHTML</abbr> document, the root <code>html</code>
1014            element must have an <code>xmlns</code> attribute as:
1015              <pre class="xml example">
1016    <code>&lt;html xmlns="http://www.w3.org/1999/xhtml"&gt;</code></pre></p></dd>
1017        <dt><code>rss</code> element</dt>
1018            <dd><p>The document is written in some version of RSS.</p>
1019            <p>The conformance checker does not support any version
1020            of RSS.  Use Atom 1.0 for feed documents.</p></dd>
1021        <dt><code>feed</code> element</dt>
1022            <dd><p>The Atom <code>feed</code> element must be
1023            in the <code>http://www.w3.org/2005/Atom</code>
1024            namespace as:
1025              <pre class="xml example">
1026    <code>&lt;feed xmlns="http://www.w3.org/2005/Atom"&gt;</code></pre>
1027            </p>
1028            <p>The conformance checker does not support Atom 0.3.
1029            Use Atom 1.0 for feed documents.</p></dd>
1030        </dl>
1031      </div>
1032    
1033    <div class="section " id="element-not-allowed:root:xml"><h3>This element is not allowed as the root element
1034      of an XML document.</h3></div>
1035    
1036    <div class="section " id="element-not-allowed:ruby-base"><h3>This element is not allowed in the <code>ruby</code>
1037      element.</h3></div>
1038    
1039    <div class="section " id="element-not-allowed:text"><h3>This element is not allowed in this
1040      context.</h3></div>
1041    
1042    <div class="section " id="element-not-allowed:atom|content"><h3>This element is not allowed in an Atom
1043      <code>content</code> element.</h3></div>
1044    
1045    <div class="section " id="element-not-allowed:atom|PersonConstruct"><h3>This element is not allowed in Person
1046      construct.</h3></div>
1047    
1048    <div class="section " id="element-not-allowed:atom|TextConstruct"><h3>This element is not allowed in Text
1049      construct.</h3></div>
1050    
1051    <div class="section " id="element-not-defined"><h3>This element is not defined.</h3></div>
1052    
1053    <div class="section " id="no-significant-content"><h3>No significant content is contained
1054      in this element.</h3></div>
1055    
1056    <div class="section " id="no-significant-content-before"><h3>There is no significant content
1057      before this element.</h3></div>
1058    
1059    <div class="section " id="no-significant-content-at-the-end"><h3>No significant content is contained
1060      at the end of this element.</h3></div>
1061    
1062    <div class="section " id="ps-element-missing"><h3>There is no <code><var>{text}</var></code>
1063      element before this element.</h3>
1064        <p>There must be an element before another element, but there
1065        is not.  The document is non-conforming.</p>
1066    
1067        <p>For example, there must be a <code>dt</code> element
1068        before any <code>dd</code> element.</p>
1069      </div>
1070    
1071    <div class="section " id="rp:syntax-error"><h3>The content of a <code>rp</code> element must
1072      be a parenthesis.</h3></div>
1073    
1074    </section>
1075    
1076    <section id="attribute-errors">
1077    <h2>Attribute Errors</h2>
1078    
1079    <div class="section " id="attribute-missing"><h3>Required attribute <code><var>{text}</var></code>
1080      is not specified.</h3>
1081        <p>A required attribute is not specified.  The document
1082        is non-conforming.</p>
1083    
1084        <p>Some attribute is defined as <i>required</i>.
1085        Without required attributes specified, user agents
1086        cannot provide full functionality of the element to the user.</p>
1087    
1088        <dl class="switch">
1089        <dt>HTML <code>img</code> element</dt>
1090            <dd>The <code>src</code> attribute must be specified.
1091            Additionally, the <code>alt</code> attribute must be specified
1092            in many cases.</dd>
1093        <dt>HTML <code>link</code> element</dt>
1094            <dd>The <code>rel</code> attribute must be specified.
1095            Note that the <code>rev</code> attribute is obsolete.</dd>
1096        </dl>
1097      </div>
1098    
1099    <div class="section " id="attribute-missing:data|type"><h3>For an <code>object</code> at least one of
1100      <code>data</code> and <code>type</code> attributes must be
1101      specified.</h3></div>
1102    
1103    <div class="section " id="attribute-missing:href|target"><h3>For a <code>base</code> element, at least one of
1104      <code>href</code> and <code>target</code> attributes must be
1105      specified.</h3></div>
1106    
1107    <div class="section " id="attribute-missing:name|http-equiv"><h3>For a <code>meta</code> element with the
1108      <code>content</code> attribute specified, exactly one of
1109      <code>name</code> and <code>http-equiv</code> attributes must be
1110      specified.</h3></div>
1111    
1112    <div class="section " id="attribute-missing:name|http-equiv|charset"><h3>For a <code>meta</code> element, exactly one of
1113      <code>name</code>, <code>http-equiv</code>, and <code>charset</code>
1114      attributes must be specified.</h3></div>
1115    
1116    <div class="section " id="attribute-not-allowed"><h3>Attribute
1117      <code><var>{local-name}</var></code> is not allowed for
1118      <code><var>{element-local-name}</var></code> element.</h3>
1119        <p>An attribute is specified where it is not allowed.
1120        The document is non-conforming.</p>
1121    
1122        <dl>
1123        <dt>HTML <code>meta</code> element</dt>
1124            <dd>For HTML <code>meta</code> element, <em>only one</em> of
1125            <code>name</code>, <code>http-equiv</code>, or <code>charset</code>
1126            attribute is allowed.</dd>
1127        </dl>
1128      </div>
1129    
1130    <div class="section " id="attribute-not-allowed:ismap"><h3>The <code>ismap</code> attribute may only be
1131      used for the image contained in an <code>a</code> element.</h3></div>
1132    
1133    <div class="section " id="attribute-not-defined"><h3>This attribute is not defined.</h3></div>
1134    
1135    <div class="section attribute-error" id="in-HTML:xml:lang"><h3>The <code>xml:lang</code> attribute is not
1136      allowed in HTML document.</h3>
1137        <p>The <code>xml:lang</code> attribute is not allowed in
1138        HTML document.  The document is non-conforming.</p>
1139    
1140        <p>Use of the <code>xml:lang</code> attribute is conforming
1141        <em>only</em> in XML documents.</p>
1142    
1143        <p>To specify natural language information in HTML document,
1144        use <code>lang</code> attribute instead.</p>
1145    
1146        <p>XHTML 1.0 Appendix C was encouraged to specify both
1147        <code>lang</code> and <code>xml:lang</code> attributes with
1148        the same value.  Such a duplication has <em>no effect</em> in practice.
1149        Use only one of <code>lang</code> (in HTML) or <code>xml:lang</code> (in
1150        XML).</p>
1151    
1152        <!-- @@ ISSUE: xml:lang in non-HTML element in DOM5 HTML created
1153             from an HTML document? -->
1154      </div>
1155    
1156    <div class="section " id="in-XML:charset"><h3>The <code>charset</code> attribute is not
1157      allowed in XML document.</h3>
1158        <p>The <code>charset</code> attribute of a
1159        <code>meta</code> element is not allowed in XML document.
1160        The document is non-conforming.</p>
1161    
1162        <p>To specify the character encoding used for serialization,
1163        if necessary, use XML declaration instead:
1164          <pre class="xml example">
1165    <code>&lt;?xml version="1.0" encoding="<var>encoding-name</var>"?&gt;</code></pre>
1166        </p>
1167      </div>
1168    
1169    <div class="section " id="in-XML:lang"><h3>The <code>lang</code> attribute is not
1170      allowed in XML document.</h3>
1171        <p>The HTML <code>lang</code> attribute is not allowed in
1172        XML document.  The document is non-conforming.</p>
1173    
1174        <p>The <code>lang</code> attribute in <code>null</code>
1175        namespace for HTML elements is conforming <em>only</em> in
1176        HTML documents.</p>
1177    
1178        <p>To specify natural language information in XML document,
1179        use <code>xml:lang</code> attribute instead.</p>
1180      </div>
1181    
1182    <div class="section " id="in-XML:noscript"><h3>A <code>noscript</code> element cannot be
1183      used in XML document.</h3></div>
1184    
1185    <div class="section " id="in-XML:xmlns"><h3>The <code>xmlns</code> attribute
1186      in the <code>null</code> namespace is not allowed in
1187      XHTML document.  The document is non-conforming.</h3>
1188        <p>The <code>xmlns</code> attribute in the <code>null</code>
1189        namespace is not allowed in XHTML document.</p>
1190    
1191        <p>This error should not occur in conformance-checking of
1192        static documents.</p>
1193      </div>
1194    
1195    </section>
1196    
1197    <section id="attribute-value-errors">
1198    <h2>Attribute Value Errors</h2>
1199    
1200    <div class="section " id="boolean:invalid"><h3>Attribute value <code><var>{@}</var></code>
1201      is not allowed.  It must be an empty string or a string
1202      <code><var>{local-name}</var></code>.</h3></div>
1203    
1204    <div class="section " id="char:syntax-error"><h3>The attribute value must be exactly one
1205      character.</h3></div>
1206    
1207    <div class="section " id="charref-in-charset"><h3>A character reference cannot be used to
1208      represent a character encoding name.</h3></div>
1209    
1210    <div class="section " id="charset:not-preferred"><h3>Character encoding name
1211      <code><var>{value}</var></code> is not the preferred name of that
1212      character encoding.</h3></div>
1213    
1214    <div class="section " id="charset:not-registered"><h3>Character encoding name
1215      <code><var>{value}</var></code> is not a registered name.</h3>
1216        <p>The specified character encoding name is not registered to
1217        <abbr>IANA</abbr>.  Use of registered character encoding name
1218        is a good practice to facilitate interoperability.</p>
1219    
1220        <dl class="switch">
1221        <dt><code>EUC-TW</code></dt>
1222          <dd><code>EUC-TW</code> is not registered.  Unfortunately, there
1223          is no registered name for that character encoding.  Use
1224          Big5 encoding with character encoding name <code>Big5</code>
1225          if it is enough to represent the document.</dd>
1226        <dt><code>ISO-2022-JP-1</code></dt>
1227          <dd><code>ISO-2022-JP-1</code> is not registered, nevertheless
1228          this character encoding name is documented in
1229          <a href="urn:ietf:rfc:2237"><abbr>RFC</abbr> 2237</a>.  Use
1230          <code>ISO-2022-JP-2</code> instead, since that character encoding
1231          is a superset of ISO-2022-JP-1.</dd>
1232        <dt><code>ISO-2022-JP-3</code>, <code>ISO-2022-JP-3-plane1</code></dt>
1233          <dd>These names are not registered and obsoleted in favor of
1234          <code>ISO-2022-JP-2004</code> and
1235          <code>ISO-2022-JP-2004-plane1</code>.</dd>
1236        <dt><code>ISO-2022-JP-2003</code>,
1237        <code>ISO-2022-JP-2003-plane1</code></dt>
1238          <dd>These names are not registered and corrected to
1239          <code>ISO-2022-JP-2004</code> and
1240          <code>ISO-2022-JP-2004-plane1</code>.</dd>
1241        <dt><code>ISO-2022-JP-2004</code>,
1242        <code>ISO-2022-JP-2004-plane1</code></dt>
1243          <dd>These names are not registered.  Unfortunately, there is
1244          no registered name for these character encodings.</dd>
1245        <dt><code>UTF-8N</code></dt>
1246          <dd><code>UTF-8N</code> is not registered.  Character encoding
1247          name <code>UTF-8</code> represents UTF-8 encoding with or
1248          without <abbr>BOM</abbr>.</dd>
1249        </dl>
1250    
1251        <p><strong>WARNING</strong>: This error might be raised for
1252        a registered character encoding name, since the character encoding
1253        name database of the conformance checker is not complete yet.</p>
1254      </div>
1255    
1256    <div class="section " id="charset:private"><h3>Character encoding name
1257      <code><var>{value}</var></code> is a private name.</h3>
1258        <p>The specified character encoding name is a private name and
1259        not registered to <abbr>IANA</abbr>.  Use of registered character
1260        encoding name is a good practice to facilitate interoperability.</p>
1261    
1262        <dl class="switch">
1263        <dt><code>x-euc-jp</code></dt>
1264          <dd>Use <code>EUC-JP</code> for the Japanese <abbr>EUC</abbr>
1265          character encoding.</dd>
1266        <dt><code>x-sjis</code></dt>
1267          <dd>Use <code>Shift_JIS</code> for standard Shift encoding scheme of
1268          <abbr>JIS</abbr> coded character set, or <code>Windows-31J</code>
1269          for Microsoft standard character set as implemented by
1270          Microsoft Windows.</dd>
1271        </dl>
1272      </div>
1273    
1274    <div class="section " id="charset:syntax-error"><h3>The specified value <code><var>{value}</var></code>
1275      is syntactically not a character encoding name.</h3>
1276        <p>The attribute value must be a character encoding name.  However,
1277        the specified value is not a character encoding name syntactically.
1278        The document is non‐conforming.</p>
1279        <p>Character encoding name is a string of <abbr>ASCII</abbr>
1280        printable characters, up to 40 characters.</p>
1281      </div>
1282    
1283    <div class="section " id="color:syntax-error"><h3>The specified value is not a color
1284      name or hexadecimal color number.</h3></div>
1285    
1286    <div class="section " id="coords:number-not-3"><h3>The <code>coords</code> attribute have to
1287      contain three (3) numbers (specified:
1288      <code><var>{text}</var></code>).</h3></div>
1289    
1290    <div class="section " id="coords:number-not-4"><h3>The <code>coords</code> attribute have to
1291      contain four (4) numbers (specified:
1292      <code><var>{text}</var></code>).</h3></div>
1293    
1294    <div class="section " id="coords:number-lt-6"><h3>The <code>coords</code> attribute have to
1295      contain more than or equal to six (6) numbers (specified:
1296      <code><var>{text}</var></code>).</h3></div>
1297    
1298    <div class="section " id="coords:number-not-even"><h3>The <code>coords</code> attribute have to
1299      contain even number of numbers (specified:
1300      <code><var>{text}</var></code>).</h3></div>
1301    
1302    <div class="section " id="coords:out-of-range"><h3>The specified value <code><var>{value}</var></code>
1303      is out of range.</h3></div>
1304    
1305    <div class="section " id="coords:syntax-error"><h3>The specified value is not valid.</h3></div>
1306    
1307    <div class="section " id="datetime:bad-year"><h3>Year number is out of range.</h3></div>
1308    
1309    <div class="section " id="datetime:bad-month"><h3>Month number is out of range.</h3></div>
1310    
1311    <div class="section " id="datetime:bad-day"><h3>Day number is out of range.</h3></div>
1312    
1313    <div class="section " id="datetime:bad-hour"><h3>Hour number is out of range.</h3></div>
1314    
1315    <div class="section " id="datetime:bad-minute"><h3>Minute number is out of range.</h3></div>
1316    
1317    <div class="section " id="datetime:bad-second"><h3>Second number is out of range.</h3></div>
1318    
1319    <div class="section " id="datetime:bad-timezone-hour"><h3>Hour number of the timezone component is out of
1320      range.</h3></div>
1321    
1322    <div class="section " id="datetime:bad-timezone-minute"><h3>Minute number of the timezone component is out of
1323      range.</h3></div>
1324    
1325    <div class="section " id="datetime:syntax-error"><h3>The attribute value is not a datetime.</h3></div>
1326    
1327    <div class="section " id="dateortime:syntax-error"><h3>The attribute value is not a date or
1328      time.</h3></div>
1329    
1330    <div class="section " id="enumerated:invalid"><h3>This attribute only allow a limited set of
1331      values and the specified value <code><var>{@}</var></code> is not one
1332      of them.</h3>
1333        <p>For this attribute only several values are allowed and the
1334        value of the attribute is not one of them.  The document
1335        is non-conforming.</p>
1336    
1337        <dl>
1338        <dt>HTML <code>meta</code> element, <code>http-equiv</code> attribute</dt>
1339            <dd><p>Only values <code>Default-Style</code> and <code>Refresh</code>
1340            are allowed.</p>
1341            <p>Value <code>Content-Type</code> is obsolete; for charset
1342            declaration, the <code>charset</code> attribute can be used as:
1343            <pre class="html example">
1344    <code>&lt;meta charset="<var>charset-name</var>"&gt;</code></pre>
1345            ... where <var>charset-name</var> is a name of the character encoding
1346            of the document, such as <code>utf-8</code>.</p>
1347            <p>Values <code>Content-Style-Type</code> and
1348            <code>Content-Script-Type</code> are currently not allowed.</p>
1349            <p>Value <code>Keywords</code> is not allowed.  Use
1350            <code>name</code> attribute instead of <code>http-equiv</code>
1351            attribute.</p>
1352            <p>Values <code>Expires</code>, <code>Pragma</code>,
1353            and <code>Cache-Control</code> are not allowed;
1354            use <em>real</em> HTTP header fields for cache control.</p></dd>
1355        </dl>
1356      </div>
1357    
1358    <div class="section attribute-value-error" id="enumerated:invalid:http-equiv:content-type"><h3>Character encoding declaration syntax
1359      <code class="html bad example">&lt;meta http-equiv="Content-Type" content="text/html; charset=<var>charset-name</var>"&gt;</code>
1360      is obsolete.</h3>
1361        <p>Old long character encoding declaration syntax
1362        <code class="html bad example">&lt;meta http-equiv="Content-Type" content="text/html; charset=<var>charset-name</var>"&gt;</code>
1363        is in use.  The document is non‐conforming.</p>
1364    
1365        <p>The new character encoding declaration syntax is:
1366          <pre class="html example">
1367    <code>&lt;meta charset="<var>charset-name</var>"&gt;</code></pre>
1368        </p>
1369      </div>
1370    
1371    <div class="section " id="enumerated:non-conforming"><h3>Attribute value <code><var>{@}</var></code>
1372      is not allowed.</h3></div>
1373    
1374    <div class="section " id="duplicate-http-equiv"><h3>There is another pragma
1375      <code><var>{value}</var></code>.</h3></div>
1376    
1377    <div class="section attribute-value-error" id="duplicate-ID"><h3>This identifier has already been
1378      assigned to another element.</h3></div>
1379    
1380    <div class="section " id="duplicate-token"><h3>The token <code><var>{value}</var></code>
1381      appears in the attribute value twice.</h3></div>
1382    
1383    <div class="section " id="empty-attribute-value"><h3>The attribute value must not be empty.</h3></div>
1384    
1385    <div class="section " id="float:out-of-range"><h3>The specified value is out of range.</h3></div>
1386    
1387    <div class="section " id="float:syntax-error"><h3>The attribute value is not a real
1388      number.</h3></div>
1389    
1390    <div class="section " id="fragment-points-itself"><h3>A fragment identifier references the element
1391      itself.</h3></div>
1392    
1393    <div class="section " id="fragment-points-nothing"><h3>A fragment identifier references no
1394      node.</h3></div>
1395    
1396    <div class="section " id="hashref:syntax-error"><h3>A hash−name reference must start with a
1397      <code>#</code> character.</h3></div>
1398    
1399    <div class="section " id="id-ne-name"><h3>The <code>id</code> attribute value is
1400      different from the <code>name</code> attribute value.</h3></div>
1401    
1402  s:URI::empty path;should;This IRI should explicitly end with <code>/</code>.  <div class="section " id="integer:syntax-error"><h3>The attribute value is not an integer.</h3></div>
1403  m:URI::syntax error;must;This IRI is not syntactically valid.  
1404    <div class="section " id="link-type:bad-context"><h3>The link type <code><var>{value}</var></code>
1405      cannot be specified for this element.</h3>
1406        <p>The specified link type cannot be used for the element.
1407        The document is non-conforming.</p>
1408    
1409        <p>Link types are associated with limited set of elements.
1410        They cannot be used with other elements.</p>
1411    
1412        <p>For example, link type <code>bookmark</code>
1413        can be used with <code>a</code> or <code>area</code> element,
1414        while it cannot be used with <code>link</code> element.</p>
1415      </div>
1416    
1417    <div class="section attribute-value-error" id="invalid-attribute-value"><h3>Attribute value <code><var>{@}</var></code>
1418      is not an allowed value.</h3></div>
1419    
1420    <div class="section " id="length:syntax-error"><h3>The attribute value is not a length
1421      value.</h3></div>
1422    
1423    <div class="section " id="link-type:non-conforming"><h3>The link type <code><var>{value}</var></code>
1424      is non-conforming.</h3>
1425        <p>The specified link type is non-conforming, and therefore
1426        the document is non-conforming.</p>
1427    
1428        <dl class="switch">
1429        <dt>Link type <code>contents</code></dt>
1430          <dd>Use link type <code>index</code>.</dd>
1431        <dt>Link type <code>copyright</code></dt>
1432          <dd>Use link type <code>license</code>.</dd>
1433        <dt>Link type <code>home</code></dt>
1434          <dd>Use link type <code>index</code>.</dd>
1435        <dt>Link type <code>previous</code></dt>
1436          <dd>Use link type <code>prev</code>.</dd>
1437        <dt>Link type <code>start</code></dt>
1438          <dd>Use link type <code>first</code>.</dd>
1439        <dt>Link type <code>toc</code> or <code>top</code></dt>
1440          <dd>Use link type <code>index</code>.</dd>
1441        </dl>
1442      </div>
1443    
1444    <div class="section " id="meta-content-type-syntax-error"><h3>The specified value is not a valid as a long
1445      character encoding declaration.</h3></div>
1446    
1447    <div class="section " id="mismatched-charset-name"><h3>The specified character encoding name
1448      <code><var>{value}</var></code> is different from the actual document
1449      character encoding <code><var>{text}</var></code>.</h3>
1450        <p>The specified character encoding name is different from
1451        the character encoding of the document.  The document
1452        is non‐conforming.</p>
1453      </div>
1454    
1455    <div class="section " id="mismatched-charset-name-not-checked"><h3>Whether the specified character encoding name
1456      <code><var>{value}</var></code> matches to the actual character encoding
1457      name cannot be checked since the input is not a byte stream.</h3></div>
1458    
1459    <div class="section " id="mode:syntax-error"><h3>The attribute value is not a valid mode
1460      name.</h3></div>
1461    
1462    <div class="section " id="nninteger:out-of-range"><h3>The specified value is out of range.</h3></div>
1463    
1464    <div class="section " id="nninteger:syntax-error"><h3>The attribute value is not a non‐negative
1465      integer.</h3></div>
1466    
1467    <div class="section " id="no-referenced-map"><h3>The <code>usemap</code> attribute references
1468      no image map.</h3></div>
1469    
1470    <div class="section " id="no-referenced-menu"><h3>The <code>contextmenu</code> attribute references
1471      no menu.</h3></div>
1472    
1473    <div class="section " id="no-referenced-header-cell"><h3>There is no table header cell whose <code>id</code>
1474      is <code><var>{value}</var></code> in the same table.</h3></div>
1475    
1476    <div class="section " id="refresh:syntax-error"><h3>the specified value is not a valid as part
1477      of a <code>Refresh</code> pragma.</h3></div>
1478    
1479    <div class="section " id="repeat:syntax-error"><h3>The attribute value is not an integer or
1480      a string <code>template</code>.</h3></div>
1481    
1482    <div class="section attribute-value-error" id="reserved-browsing-context-name"><h3>Browsing context name
1483      <code><var>{@}</var></code> is reserved.</h3>
1484        <p>The specified browsing context name is reserved.
1485        The document is non-conforming.</p>
1486    
1487        <p>Names of browsing contexts starting with <code>_</code>
1488        (<code>U+005F</code> <code class="charname">LOW LINE</code>)
1489        are reserved so that it must not be used.</p>
1490    
1491        <p>Old version of HTML, non-HTML markup languages, and
1492        Web browsers define or implements special reserved
1493        browsing context names <code>_blank</code>,
1494        <code>_main</code>, and <code>_replace</code>.
1495        However, they are <em>not</em> conforming attribute values.</p>
1496      </div>
1497    
1498    <div class="section " id="Reserved-Prefixes-and-Namespace-Names:Name"><h3>Namespace name <code><var>{text}</var></code>
1499      is reserved and cannot be used for an arbitrary prefix.</h3></div>
1500    
1501    <div class="section " id="Reserved-Prefixes-and-Namespace-Names:Prefix"><h3>Namespace prefix <code><var>{text}</var></code>
1502      is reserved and cannot be used for an arbitrary namespace name.</h3></div>
1503    
1504    <div class="section " id="link-type:proposed"><h3>Link type <code><var>{value}</var></code>
1505      is proposed but not accepted yet; it <em>should not</em> be
1506      used until it has been accepted.</h3>
1507        <p>The link type is in the <i>proposed</i> status; it
1508        <em>should not</em> be used until it has been
1509        accepted.</p>
1510    
1511        <p><strong>Warning</strong>: The data served to the
1512        conforming checker might be out of date; it might have already
1513        been accepted or rejected.  The document might or might not be
1514        conforming depending on the status.  See WHATWG Wiki
1515        for the latest information.</p>
1516      </div>
1517    
1518    <div class="section " id="sizes:syntax-error"><h3>The specified value <code><var>{value}</var></code>
1519      is not a valid value.</h3></div>
1520    
1521    <div class="section " id="space-in-ID"><h3>White space characters are not allowed
1522      in the <code>id</code> attribute.</h3></div>
1523    
1524    <div class="section " id="template:not-template"><h3>The node referenced by the <code>template</code>
1525      attribute is not a template.</h3></div>
1526    
1527    <div class="section " id="window-name:empty"><h3>Browsing context name must not be empty.</h3></div>
1528    
1529    <div class="section " id="window-name:reserved"><h3>Browsing context name
1530      <code><var>{value}</var></code> is reserved.</h3></div>
1531    
1532    <div class="section " id="word-not-allowed"><h3>The word <code><var>{value}</var></code> is not
1533      allowed in this attribute.</h3></div>
1534    
1535    <div class="section " id="XML-1.0-NCName:syntax-error"><h3>The specified value is not a legal XML Namespaces
1536      1.0 <code>NCName</code>.</h3></div>
1537    
1538    </section>
1539    
1540    <section id="table-model-errors">
1541    <h2>Table Model Errors</h2>
1542    
1543    <div class="section " id="cell-overlapping"><h3>Cell slot (<var>{text}</var>) is filled by
1544      multiple cells.</h3></div>
1545    
1546    <div class="section " id="colspan-creates-column-with-no-anchored-cell"><h3>This <code>colspan</code> attribute
1547      results in creating a table column that does not contain
1548      any cell anchored to it.</h3></div>
1549    
1550    <div class="section " id="column-with-no-anchored-cell"><h3>This column has no anchored cell.</h3></div>
1551    
1552    <div class="section table-model-error" id="table:no-cell-in-last-row"><h3>The table has no cell (<code>td</code> or
1553      <code>th</code>) in the last row.</h3></div>
1554    
1555    <div class="section table-model-error" id="table:rowspan-extends-table"><h3>This <code>rowspan</code> attribute
1556      results in creating a table row that does not contain
1557      any cell anchored to it.</h3>
1558        <p>The <code>rowspan</code> attribute value of the cell
1559        is so specified that it extends a table in the row axis.
1560        However, the extended row does not contain any cell by itself.
1561        The document is non-conforming.</p>
1562    
1563        <p>For example, the table below is non-conforming:
1564          <pre class="html bad example">
1565    <code>&lt;table&gt;
1566    &lt;tbody&gt;
1567    &lt;tr&gt;&lt;td rowspan=2&gt;&lt;/td&gt;&lt;/tr&gt;
1568    &lt;/tbody&gt;
1569    &lt;/table&gt;</code></pre>
1570        ... since the second row contains only
1571        a cell that spans between first and second rows.</p>
1572      </div>
1573    
1574    <div class="section " id="row-with-no-anchored-cell"><h3>This row has no anchored cell.</h3></div>
1575    
1576    <div class="section " id="rowspan-creates-row-with-no-anchored-cell"><h3>This <code>rowspan</code> attribute
1577      results in creating a table row that does not contain
1578      any cell anchored to it.</h3></div>
1579    
1580    
1581    </section>
1582    
1583    <section id="imt-warnings">
1584    <h2>Internet Media Type Errors</h2>
1585    
1586    <div class="section " id="IMT:composite"><h3>The specified media type is a composite
1587      type, which is not allowed in this context.</h3></div>
1588    
1589    <div class="section " id="IMT:syntax-error"><h3>The specified value is not an Internet Media
1590      Type.</h3></div>
1591    
1592    <div class="section should" id="s:IMT:obsolete-subtype"><h3><code><var>{@}</var></code>: An <em>obsolete</em>
1593      subtype is used.</h3></div>
1594    
1595    <div class="section should" id="s:IMT:private-subtype"><h3><code><var>{@}</var></code>: A private
1596      (<code>x-</code> or <code>x.</code>) subtype is used.</h3></div>
1597    
1598    <div class="section should" id="s:IMT:unregistered-subtype"><h3><code><var>{@}</var></code>: The subtype is
1599      not registered to IANA.</h3></div>
1600    
1601    <div class="section " id="not-IMT"><h3>A value that is not an Internet Media Type
1602      is not allowed here.</h3></div>
1603    
1604    </section>
1605    
1606    <section id="uri-errors">
1607    <h2>URI (or IRI) Errors</h2>
1608    
1609    <div class="section must" id="m:URI::syntax-error"><h3>The specified value is syntactically not an IRI
1610      reference.</h3>
1611        <p>The specified value does not satisfy the syntactical requirements
1612        for IRI references.  The document is non-conforming.</p>
1613    
1614        <p>Possible causes:
1615          <ul>
1616          <li>The string might contain one or more white space characters.
1617          Especially, the <code> </code> (<code>U+0020</code>
1618          <code class="charname">SPACE</code>) character cannot be
1619          used in IRI references.</li>
1620          </ul>
1621        </p>
1622      </div>
1623    
1624    </section>
1625    
1626    <section id="uri-shoulds">
1627    <h2>URI (or IRI) Should-level Errors</h2>
1628    
1629    <div class="section should" id="s:URI::dot-segment"><h3>A dot-segment (<code>.</code> or
1630      <code>..</code>) occurs in an absolute reference.</h3>
1631        <p>Dot-segment (<code>.</code> or <code>..</code>) should
1632        not occur in an absolute reference.</p>
1633    
1634        <p>In relative references, dot-segments are used to represent
1635        the current (<code>.</code>) or the parent (<code>..</code>)
1636        hierarchy of the path.  Though they are also allowed
1637        in absolute references, it should be resolved to the
1638        canonical form before it has been published.</p>
1639      </div>
1640    
1641    <div class="section should" id="s:URI::empty-path"><h3>This IRI does not end with
1642      a <code>/</code>.</h3></div>
1643    
1644    <div class="section should" id="s:URI::lowercase-hexadecimal-digit"><h3>A lowercase hexadecimal digit is used
1645      in percent-encoding.</h3>
1646        <p>The hexadecimal digit in percent-encoding string in the IRI
1647        is in lowercase.  Though the IRI <em>is</em> conforming,
1648        it should be in uppercase.</p>
1649      </div>
1650    
1651    <div class="section should" id="s:URI::percent-encoded-unreserved"><h3>An unreserved character is
1652      percent-encoded.</h3>
1653        <p>An unreserved character is percent-encoded in the IRI.
1654        Though it <em>is</em> conforming, it should be in the
1655        decoded (or bare) form.</p>
1656      </div>
1657    
1658    <div class="section should" id="s:URI::uppercase-scheme-name"><h3>URI scheme name is in uppercase.</h3>
1659        <p>The scheme part of the IRI is written in uppercase letter.</p>
1660    
1661        <p>Uppercase scheme names are not required to be processed
1662        correctly.</p>
1663    <!-- @@
1664     RFC 3986 3.1.
1665     > Although schemes are case-
1666       insensitive, the canonical form is lowercase and documents that
1667       specify schemes must do so with lowercase letters.
1668    
1669     > An implementation ... should only produce lowercase scheme names for
1670       consistency.
1671    -->
1672      </div>
1673    
1674    </section>
1675    
1676    <section id="cache-manifest-errors">
1677    <h2>Cache Manifest Errors</h2>
1678    
1679    <div class="section must" id="m:not-manifest"><h3>This document is not a cache manifest.</h3>
1680        <p>The specified document is <em>not</em> a cache manifest.
1681        The document is non-conforming.</p>
1682    
1683        <p>An entity labeled as Internet media type
1684        <code>text/cache-manifest</code> must contain a cache manifest.</p>
1685    
1686        <p>A cache manifest must start with a line whose content is
1687        <code class="manifest example">CACHE MANIFEST</code>
1688        (exactly one space character between
1689        <code>CACHE</code> and <code>MANIFEST</code>).</p>
1690      </div>
1691    </section>
1692    
1693    <section id="information">
1694    <h2>Stability Information</h2>
1695    
1696    <div class="section " id="deprecated:attr"><h3>This attribute is deprecated.</h3></div>
1697    
1698    <div class="section " id="deprecated:element"><h3>This element is deprecated.</h3></div>
1699    
1700    <div class="section " id="status:cr:element"><h3>This element is in the
1701      <strong>call for implementation</strong> stage.</h3>
1702        <p>The element is in the call for implementation stage.</p>
1703        
1704        <p>Usually, using the element is safe.  However, it is a new feature
1705        so that it might not be implemented correctly.  If it is found that
1706        the feature is hard or impossible to implement, the feature
1707        might be revised, or in some case it might be dropped.</p>
1708    
1709        <p>Elements defined by Atom 1.0 (IETF Proposed Standard), and XBL 2.0
1710        (W3C Candidate Recommendation) belong to this class.</p>
1711      </div>
1712    
1713    <div class="section " id="status:lc:element"><h3>This element is in the <strong>last
1714      call for comments</strong> stage.</h3>
1715        <p>The element is in the last call for comments stage.</p>
1716        
1717        <p>The element is relatively mature, though the standardization
1718        is not done yet.  It may be used for experiments.  Since it is a new
1719        feature, it might not be implemented correctly or at all.  If it is
1720        found that the feature is hard or impossible to implement, the feature
1721        might be revised or might be dropped.</p>
1722    
1723        <p>Elements defined by Web Forms 2.0 as well as some elements
1724        defined by HTML5 belong to this class.</p>
1725      </div>
1726    
1727    <div class="section " id="status:wd:element"><h3>This element is documented in a <strong>working
1728      draft</strong>.</h3>
1729        <p>The element is documented in a working or editor's draft
1730        and not yet completed.</p>
1731        
1732        <p>The element should not be used for any practical purpose.
1733        The feature might be drastically changed later or might be
1734        entirely removed.</p>
1735    
1736        <p>Most of new elements defined by HTML5 belong to this class.</p>
1737      </div>
1738    
1739    <div class="section " id="status:non-standard:element"><h3>This element is <strong>not part of any
1740      standard</strong> the conformance checker knows.</h3>
1741        <p>The element is not part of any standard or draft the conformance
1742        checker is aware of.</p>
1743        
1744        <p>The element should not be used for any practical purpose unless
1745        there is really a standard that defines the element.</p>
1746      </div>
1747    
1748    <div class="section " id="status:cr:attr"><h3>This attribute is in the
1749      <strong>call for implementation</strong> stage.</h3>
1750        <p>The attribute is in the call for implementation stage.</p>
1751        
1752        <p>Usually, using the attribute is safe.  However, it is a new feature
1753        so that it might not be implemented correctly.  If it is found that
1754        the feature is hard or impossible to implement, the feature
1755        might be revised, or in some case it might be dropped.</p>
1756      </div>
1757    
1758    <div class="section " id="status:lc:attr"><h3>This attribute is in the <strong>last
1759      call for comments</strong> stage.</h3>
1760        <p>The attribute is in the last call for comments stage.</p>
1761        
1762        <p>The attribute is relatively mature, though the standardization
1763        is not done yet.  It may be used for experiments.  Since it is a new
1764        feature, it might not be implemented correctly or at all.  If it is
1765        found that the feature is hard or impossible to implement, the feature
1766        might be revised or might be dropped.</p>
1767      </div>
1768    
1769    <div class="section " id="status:wd:attr"><h3>This attribute is documented in a <strong>working
1770      draft</strong>.</h3>
1771        <p>The attribute is documented in a working or editor's draft
1772        and not yet completed.</p>
1773        
1774        <p>The attribute should not be used for any practical purpose.
1775        The feature might be drastically changed later or might be
1776        entirely removed.</p>
1777      </div>
1778    
1779    <div class="section " id="status:non-standard:attr"><h3>This attribute is <strong>not part of any
1780      standard</strong> the conformance checker knows.</h3>
1781        <p>The attribute is not part of any standard or draft the conformance
1782        checker is aware of.</p>
1783        
1784        <p>The attribute should not be used for any practical purpose unless
1785        there is really a standard that defines the attribute.</p>
1786      </div>
1787    </section>
1788    
1789    <section id="rdfxml-errors">
1790    <h2>RDF/XML Errors</h2>
1791    
1792    <div class="section " id="bad-rdf-namespace"><h3>The namespace URI of an element that
1793      represents an RDF concept must be
1794      <code>http://www.w3.org/1999/02/22-rdf-syntax-ns#</code>.</h3></div>
1795    
1796    <div class="section " id="duplicate-rdf-id"><h3>The specified value is already used as an
1797      ID.</h3></div>
1798    
1799    <div class="section " id="duplicate-unqualified-attr"><h3>Both unqualified attribute and namespace‐qualified
1800      RDF attribute are specified, which is not allowed.</h3></div>
1801    
1802    <div class="section " id="parse-type-other"><h3>An invalid value is specified to
1803      the <code>parseType</code> attribute.</h3></div>
1804    
1805    <div class="section " id="second-node-element"><h3>There is another element, such that
1806      this element is not allowed.</h3></div>
1807    
1808    <div class="section " id="unqualified-attr"><h3>Unqualified attribute is not allowed.</h3></div>
1809    
1810    <div class="section " id="unqualified-rdf-attr"><h3>RDF attribute should be
1811      namespace‐qualified.</h3></div>
1812    
1813  </section>  </section>
1814    
1815  <section id="unsupported-messages">  <section id="unsupported-messages">
1816  <h2><i>Unsupported</i> Messages</h2>  <h2><i>Unsupported</i> Messages</h2>
1817    
1818  <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
1819    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
1820      <p>The conformant checker does not support the attribute.    might not be conforming</em>.</h3>
1821        <p>The conformant checker does not support the element.
1822      It cannot determine whether the document is conforming or not.</p>      It cannot determine whether the document is conforming or not.</p>
1823    </div>    </div>
1824    
1825  <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
1826    conformance checker; <em>it might or might not be conforming</em>.</h3>    <code><var>{local-name}</var></code> of element
1827      <p>The conformant checker does not support the element.    <code><var>{element-local-name}</var></code> is not supported;
1828      <em>it might or might not be conforming</em>.</h3>
1829        <p>The conformant checker does not support the attribute.
1830      It cannot determine whether the document is conforming or not.</p>      It cannot determine whether the document is conforming or not.</p>
1831    </div>    </div>
1832    
1833  <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
1834    or registered at the time of the release of the conformance checker;    standardized or registered at the time of the release of the conformance
1835    <em>it is non-conforming unless it has now been registered</em>.</h3>    checker; <em>it is non-conforming unless it now has been
1836      registered</em>.</h3>
1837      <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.
1838      Some common link types are defined in the HTML5 specification.      Some common link types are defined in the HTML5 specification.
1839      Additional link types can be registered to the WHATWG Wiki.      Additional link types can be registered to the WHATWG Wiki.
# Line 172  m:URI::syntax error;must;This IRI is not Line 1844  m:URI::syntax error;must;This IRI is not
1844      The link type might have been added to the registry since then.      The link type might have been added to the registry since then.
1845      In such case it might be conforming.  Otherwise, the      In such case it might be conforming.  Otherwise, the
1846      document is non-conforming.</p>      document is non-conforming.</p>
1847    
1848        <dl>
1849        <dt>Link types <code>shortcut icon</code></dt>
1850            <dd>Link type <code>shortcut</code> is not registered.
1851            Use only <code>icon</code> for linking to so-called favicon.</dd>
1852        </dl>
1853    </div>    </div>
1854    
1855    <div class="section " id="event-handler"><h3>Conformance checking for event handler attribute
1856      is not supported; <em>it might or might not be conforming.</em></h3></div>
1857    
1858    <div class="section " id="media-query"><h3>Conformance checking for media query
1859      is not supported; <em>it might or might not be conforming.</em></h3></div>
1860    
1861    <div class="section " id="addr-spec-not-supported"><h3>Conformance checking for an <code>addr-spec</code>
1862      is not supported; <em>it might or might not be conforming.</em></h3></div>
1863    
1864    <div class="section " id="XML-script-lang"><h3>Conformance checking for script
1865      language <code><var>{text}</var></code> is not supported;
1866      <em>it might or might not be conforming.</em></h3></div>
1867    
1868    <div class="section " id="XML-style-lang"><h3>Conformance checking for style
1869      language <code><var>{text}</var></code> is not supported;
1870      <em>it might or might not be conforming.</em></h3></div>
1871    
1872    <div class="section " id="atom|content-not-supported"><h3>Conformance checking for an Atom
1873      <code>content</code> element with <code>type</code>
1874      <code><var>{text}</var></code> is not supported.</h3></div>
1875    
1876    </section>
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2082    
2083    
2084    <section id="levels">
2085    <h2>Error Levels</h2>
2086    
2087    <table id="levels-table">
2088    <thead>
2089    <tr><th scope="col">Level</th>
2090    <th scope="col">Conforming?</th>
2091    <th scope="col">Description</th>
2092    </tr>
2093    </thead>
2094    <tbody>
2095    <tr class="level-m" id="level-m">
2096    <th scope="row"><em class="rfc2119">MUST</em>‐level error</th>
2097    <td>Non‐conforming.</td>
2098    <td>A violation to a hard requirement of the specification.
2099    The document is non‐conforming.</td>
2100    </tr>
2101    <tr class="level-s" id="level-s">
2102    <th scope="row"><em class="rfc2119">SHOULD</em>‐level error</th>
2103    <td>Non‐conforming, but <em>in some case</em>
2104    conforming.</td>
2105    <td>A violation to a requirement of the specification.
2106    The violation might be legitimize in some case.  Otherwise,
2107    the document is non‐conforming.</td>
2108    </tr>
2109    <tr class="level-w" id="level-w">
2110    <th scope="row">Warning</th>
2111    <td>Conforming.</td>
2112    <td>A warning is an advice from the conformance checker to avoid
2113    to solve a problem in a confusing or possibly wrong way.
2114    It does not affect to the conformance of the document, and
2115    may sometimes be inappropriate.</td>
2116    </tr>
2117    <tr class="level-i" id="level-i">
2118    <th scope="row">Information</th>
2119    <td>Conforming.</td>
2120    <td>An informational message just provides an additional information
2121    on the feature used in the document or the status of the retrieval
2122    or so on.
2123    It does not affect to the conformance of the document.</td>
2124    </tr>
2125    <tr class="level-u" id="level-u">
2126    <th scope="row">Not supported</th>
2127    <td><em>Unknown</em>.</td>
2128    <td>Some feature that is not supported by the conformance checker
2129    is used in the document.</td>
2130    </tr>
2131    </tbody>
2132    </table>
2133  </section>  </section>
2134    
2135  <section id="license">  <section id="license">
2136  <h2>License of This Document</h2>  <h2>License of This Document</h2>
2137    
2138  <p>Copyright 2007 <a href="http://suika.fam.cx/~wakaba/who?">Wakaba</a></p>  <p>Copyright <time>2007</time>‐<time>2008</time>
2139  <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>
2140    <code class="mail">&lt;<a href="mailto:[email protected]">[email protected]</a>&gt;</code>.</p>
2141    
2142    <p>This document is free software; you can redistribute it
2143  and/or modify it under the same terms as Perl itself.</p>  and/or modify it under the same terms as Perl itself.</p>
2144  </section>  </section>
2145    
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