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revision 1.2 by wakaba, Mon Jul 16 08:38:48 2007 UTC revision 1.29 by wakaba, Sat Aug 16 07:42:20 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="character-encoding-layer">
12    <h2>Character Encoding Layer Errors</h2>
13    
14    <div class="section error-category-charset" id="m:illegal-octets-error"><h3>An illegal octet in the input stream.</h3></div>
15    </section>
16    
17    <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">  <section id="html5-tokenize-error">
153  <h2>HTML5 Parse Errors in Tokenization Stage</h2>  <h2>HTML5 Parse Errors in Tokenization Stage</h2>
154    
155  <div class="section tokenize-error" id="duplicate-attribute"><h3>There are two attributes with same name.</h3>  <div class="section parse-error" id="after-html"><h3>Tag <code>&lt;<var>$0</var>&gt;</code>
156      <p>Attributes must be unique in an element.  Specifying    is not allowed after the end tag <code>&lt;/html&gt;</code>.</h3>
157      attributes with same name more than once is non-conforming.</p>      <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>
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>
334    
335    <div class="section tokenize-error" id="bogus-end-tag"><h3>String <code>&lt;/</code> is not followed
336      by tag name.</h3>
337        <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>  </section>
541    
542  <section id="html5-parse-errors">  <section id="html5-parse-errors">
543  <h2>HTML5 Parse Errors in Tree Construction Stage</h2>  <h2>HTML5 Parse Errors in Tree Construction Stage</h2>
544    
545  <div class="section parse-error" id="after-head"><h3>The <code><var>$0</var></code> element cannot be  <div class="section parse-error" id="after-body"><h3>Start tag <code>&lt;<var>{text}</var>&gt;</code> is
546    inserted between <code>head</code> and <code>body</code> elements.</h3>    not allowed after the <code>body</code> is closed.</h3></div>
547      <p>A start tag occurs after the <code>head</code> element is closed  
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.      but before the <code>body</code> element is opened.
568      The document is non-conforming.</p>      The document is non-conforming.</p>
569    </div>    </div>
570    
571  <div class="section parse-error" id="no-DOCTYPE"><h3>This document does not start with the  <div class="section parse-error" id="after-html"><h3>Start tag <code>&lt;<var>{text}</var>&gt;</code> is
572    <code>DOCTYPE</code> declaration.</h3></div>    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="not-closed"><h3>Element <code><var>$0</var></code> is not  <div class="section parse-error" id="isindex"><h3>The <code>isindex</code> element is
696    closed.</h3></div>    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  <div class="section parse-error" id="not-HTML5"><h3>This document is written in an old version of
769    HTML.</h3></div>    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>$0</var></code> is not  <div class="section parse-error" id="unmatched-end-tag"><h3>Element <code><var>{text}</var></code> is not
786    opened.</h3></div>    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    <div class="section " id="element-not-allowed:area"><h3>An <code>area</code> element cannot be used
958      outside of a <code>map</code> element.</h3></div>
959    
960    <div class="section " id="element-not-allowed:base"><h3>There is another <code>base</code>
961      element.</h3></div>
962    
963    <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    
966    <div class="section " id="element-not-allowed:details-legend"><h3>In a <code>details</code> element, only at the
967      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>  </section>
1196    
1197  <section id="attribute-value-errors">  <section id="attribute-value-errors">
1198  <h2>Attribute Value Errors</h2>  <h2>Attribute Value Errors</h2>
1199    
1200  <div class="section attribute-error" id="enumerated:invalid"><h3>This attribute only allow a limited set of  <div class="section " id="boolean:invalid"><h3>Attribute value <code><var>{@}</var></code>
1201    values and the specified value is not one of them.</h3></div>    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    <div class="section " id="integer:syntax-error"><h3>The attribute value is not an integer.</h3></div>
1403    
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>  </section>
1539    
1540  <section id="table-model-errors">  <section id="table-model-errors">
1541  <h2>Table Model Errors</h2>  <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  <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>    <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>  </section>
1582    
1583  <section id="imt-warnings">  <section id="imt-warnings">
1584  <h2>Internet Media Type Warnings</h2>  <h2>Internet Media Type Errors</h2>
1585    
1586  <div class="section should" id="s:IMT:obsolete-subtype"><h3>An <em>obsolete</em> subtype is used.</h3></div>  <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 should" id="s:IMT:private-subtype"><h3>A private (<code>x-</code> or <code>x.</code>)  <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>    subtype is used.</h3></div>
1594    
1595  <div class="section should" id="s:IMT:unregistered-subtype"><h3>The subtype is not registered to IANA.</h3></div>  <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>  </section>
1605    
1606  <section id="uri-errors">  <section id="uri-errors">
1607  <h2>URI (or IRI) Errors</h2>  <h2>URL Errors</h2>
1608    
1609    <div class="section " id="syntax-error:iri3987"><h3>The specified value is syntactically not an
1610      IRI.</h3></div>
1611    
1612    <div class="section " id="syntax-error:iriref3987"><h3>The specified value is syntactically not an IRI
1613      reference.</h3>
1614        <p>The specified value does not satisfy the syntactical requirements
1615        for IRI references.  The document is non-conforming.</p>
1616    
1617  <div class="section must" id="m:URI::syntax-error"><h3>This string is not an IRI syntactically.</h3></div>      <p>Possible causes:
1618          <ul>
1619          <li>The string might contain one or more white space characters.
1620          Especially, the <code> </code> (<code>U+0020</code>
1621          <code class="charname">SPACE</code>) character cannot be
1622          used in IRI references.</li>
1623          </ul>
1624        </p>
1625      </div>
1626    
1627    <div class="section " id="syntax-error:rdfuriref"><h3>The specified value is syntactically not an RDF
1628      URI reference.</h3></div>
1629    
1630    <div class="section " id="syntax-error:uri2396"><h3>The specified value is syntactically not a
1631      URI according to RFC 2396.</h3></div>
1632    
1633    <div class="section " id="syntax-error:uri3986"><h3>The specified value is syntactically not a
1634      URI.</h3></div>
1635    
1636    <div class="section " id="URL:address-format"><h3>URL host address format
1637      <code><var>{value}</var></code> is not supported by the
1638      conformance checker.</h3></div>
1639    
1640    <div class="section " id="URL:default-port"><h3>Default port number should be omitted.</h3></div>
1641    
1642    <div class="section " id="URL:dot-segment"><h3>A dot-segment (<code>.</code> or
1643      <code>..</code>) occurs in an absolute reference.</h3>
1644        <p>Dot-segment (<code>.</code> or <code>..</code>) should
1645        not occur in an absolute reference.</p>
1646    
1647        <p>In relative references, dot-segments are used to represent
1648        the current (<code>.</code>) or the parent (<code>..</code>)
1649        hierarchy of the path.  Though they are also allowed
1650        in absolute references, it should be resolved to the
1651        canonical form before it has been published.</p>
1652      </div>
1653    
1654    <div class="section " id="URL:empty-host"><h3>The host component of the URL is empty.</h3></div>
1655    
1656    <div class="section " id="URL:empty-path"><h3>The URL does not end with
1657      a <code>/</code> character.</h3></div>
1658    
1659    <div class="section " id="URL:empty-port"><h3>The port component of the URL is empty.</h3></div>
1660    
1661    <div class="section " id="URL-fragment-not-allowed"><h3>The fragment component of the URL is not
1662      allowed.</h3></div>
1663    
1664    <div class="section " id="URL:long-host"><h3>The host component of the URL
1665      is too long.</h3></div>
1666    
1667    <div class="section " id="URL:lowercase-hexadecimal-digit"><h3>A lowercase hexadecimal digit is used
1668      in percent-encoding.</h3>
1669        <p>The hexadecimal digit in percent-encoding string in the IRI
1670        is in lowercase.  Though the IRI <em>is</em> conforming,
1671        it should be in uppercase.</p>
1672      </div>
1673    
1674    <div class="section " id="URL:non-DNS-host"><h3>The host component of the URL
1675      is not a DNS host name.</h3></div>
1676    
1677    <div class="section " id="URL:non-UTF-8-host"><h3>The host component of the URL
1678      is not encoded in UTF-8.</h3></div>
1679    
1680    <div class="section " id="URL:password"><h3>Password should not be included in a URL
1681      for the security.</h3></div>
1682    
1683    <div class="section " id="URL:percent-encoded-unreserved"><h3>An unreserved character is
1684      percent-encoded.</h3>
1685        <p>An unreserved character is percent-encoded in the IRI.
1686        Though it <em>is</em> conforming, it should be in the
1687        decoded (or bare) form.</p>
1688      </div>
1689    
1690    <div class="section " id="URL:uppercase-host"><h3>The host <code><var>{value}</var></code>
1691      should be spelt in lowercase.</h3></div>
1692    
1693    <div class="section " id="URL:uppercase-scheme-name"><h3>URL scheme name is in uppercase.</h3>
1694        <p>The scheme part of the IRI is written in uppercase letter.</p>
1695    
1696        <p>Uppercase scheme names are not required to be processed
1697        correctly.</p>
1698    <!-- @@
1699     RFC 3986 3.1.
1700     > Although schemes are case-
1701       insensitive, the canonical form is lowercase and documents that
1702       specify schemes must do so with lowercase letters.
1703    
1704     > An implementation ... should only produce lowercase scheme names for
1705       consistency.
1706    -->
1707      </div>
1708    
1709  </section>  </section>
1710    
1711  <section id="uri-errors">  <section id="mq-errors">
1712  <h2>URI (or IRI) Errors</h2>  <h2>Media Query Errors</h2>
1713    
1714    <div class="section " id="mq-syntax-error"><h3>The specified value has a syntax error as a
1715      media query.</h3></div>
1716    
1717    <div class="section " id="unknown-media-type"><h3>Media type <code><var>{value}</var></code> is
1718      not supported by the conformance checker.</h3></div>
1719    
1720    </section>
1721    
1722    <section id="selectors-errors">
1723    <h2>Selectors Errors</h2>
1724    
1725    <div class="section " id="an+b-not-closed"><h3>Argument list of the pseudo-class is
1726      not closed by a <code>)</code> character.</h3></div>
1727    
1728    <div class="section " id="ab+b-not-integer"><h3>Numbers in the argument
1729      <code><var>a</var>n+<var>b</var></code> have to be integers.</h3></div>
1730    
1731    <div class="section " id="an+b-syntax-error"><h3>Argument <code><var>a</var>n+<var>b</var></code> is
1732      syntactically incorrect.</h3></div>
1733    
1734    <div class="section " id="attr-selector-not-closed"><h3>Attribute selector is not closed by
1735      a <code>]</code> character.</h3></div>
1736    
1737    <div class="section " id="lang-selector-not-closed"><h3>Argument list of the <code>:lang</code>
1738      selector is not closed by a <code>)</code> character.</h3></div>
1739    
1740    <div class="section " id="namespace-prefix:not-declared"><h3>Namespace prefix <code><var>{value}</var></code>
1741      is not declared.</h3></div>
1742    
1743    <div class="section " id="no-attr-local-name"><h3>Attribute local name is missing.</h3></div>
1744    
1745    <div class="section " id="no-attr-match"><h3>Attribute matching operator (e.g.
1746      <code>=</code>) is missing.</h3></div>
1747    
1748    <div class="section " id="no-attr-name"><h3>Attribute name is missing.</h3></div>
1749    
1750    <div class="section " id="no-attr-namespace-separator"><h3>Attribute namespace wildcard <code>*</code>
1751      is not followed by a <code>|</code> character.</h3></div>
1752    
1753    <div class="section " id="no-attr-value"><h3>Attribute value is missing.</h3></div>
1754    
1755    <div class="section " id="no-class-name-selector"><h3>Class name is missing.</h3></div>
1756    
1757    <div class="section " id="no-combinator"><h3>Combinator is missing.</h3></div>
1758    
1759    <div class="section " id="no-contains-string"><h3>No string is specified in the argument
1760      list of the <code>:-manakai-contains</code> pseudo-class
1761      selector.</h3></div>
1762    
1763    <div class="section " id="no-lang-tag"><h3>Language tag argument is missing.</h3></div>
1764    
1765    <div class="section " id="no-local-name-selector"><h3>Local name part of the type selector (or
1766      <code>*</code> for the universal selector) is missing.</h3></div>
1767    
1768    <div class="section " id="no-pseudo-class-name"><h3>Pseudo-class name is missing.</h3></div>
1769    
1770    <div class="section " id="no-pseudo-element-name"><h3>Pseudo-element name is missing.</h3></div>
1771    
1772    <div class="section " id="no-sss"><h3>Sequence of simple selectors is
1773      expected.</h3></div>
1774    
1775    <div class="section " id="not-not-closed"><h3>Argument list of the <code>:not</code> selector
1776      is not closed by a <code>)</code> character.</h3></div>
1777    
1778    <div class="section " id="ss-after-pseudo-element"><h3>Simple selector is not allowed after a
1779      pseudo element.</h3></div>
1780    
1781    <div class="section " id="unknown-pseudo-class"><h3>Pseudo-class <code>:<var>{value}</var></code>
1782      is not supported by the conformance checker.</h3></div>
1783    
1784    <div class="section " id="unknown-pseudo-element"><h3>Pseudo-element <code>::<var>{value}</var></code>
1785      is not supported by the conformance checker.</h3></div>
1786    
1787    </section>
1788    
1789    <section id="css-errors">
1790    <h2>CSS Errors</h2>
1791    
1792    <div class="section " id="at-rule-not-allowed"><h3>An <code>@<var>{text}</var></code> rule is not
1793      allowed here.</h3></div>
1794    
1795    <div class="section " id="at-rule-syntax-error"><h3>The <code>@<var>{text}</var></code> rule is
1796      syntactically incorrect.</h3></div>
1797    
1798    <div class="section " id="block-not-closed"><h3>Block is not closed before the end of
1799      file.</h3></div>
1800    
1801    <div class="section " id="CSS-duplication"><h3>Component <code>&lt;<var>{text}</var>&gt;</code> is
1802      already specified.</h3></div>
1803    
1804    <div class="section " id="CSS-syntax-error"><h3>Specified value is syntactically not a correct
1805      <code>&lt;<var>{text}</var>&gt;</code>.</h3></div>
1806    
1807    <div class="section " id="no-declaration-block"><h3>No declaration block is found after a group of
1808      selectors.</h3></div>
1809    
1810    <div class="section " id="no-property-colon"><h3>A <code>:</code> character is missing after
1811      a property name.</h3></div>
1812    
1813    <div class="section " id="no-property-name"><h3>Property name is expected.</h3></div>
1814    
1815    <div class="section " id="no-property-semicolon"><h3>A <code>;</code> character is missing at the
1816      end of the property.</h3></div>
1817    
1818    <div class="section " id="priority-syntax-error"><h3>Priority part of the declaration is syntactically
1819      incorrect.</h3></div>
1820    
1821    <div class="section " id="unknown-at-rule"><h3>The <code>@<var>{value}</var></code> rule is
1822      not supported by the conformance checker.</h3></div>
1823    
1824    <div class="section " id="unknown-property"><h3>Property <code><var>{value}</var></code> is
1825      not supported by the conformance checker.</h3></div>
1826    
1827    </section>
1828    
1829    <section id="cache-manifest-errors">
1830    <h2>Cache Manifest Errors</h2>
1831    
1832    <div class="section " id="both-in-entries-and-whitelist"><h3>This URL is found both in the explicit or
1833      fallback entries and in the online whitelist.</h3></div>
1834    
1835    <div class="section " id="different-origin-from-manifest"><h3>The specified URL has different origin from
1836      the manifest.</h3></div>
1837    
1838    <div class="section " id="different-scheme-from-manifest"><h3>The scheme component of the URL is
1839      different from that of the manifest URL.  The URL is ignored.</h3></div>
1840    
1841    <div class="section " id="duplicate-oc-namespace"><h3>This oppotunistic caching namespace is already
1842      specified.</h3></div>
1843    
1844    <div class="section " id="no-fallback-entry-URL"><h3>Fallback entry URL is missing.</h3></div>
1845    
1846    <div class="section " id="not-manifest"><h3>This document is not a cache manifest.</h3>
1847        <p>The specified document is <em>not</em> a cache manifest.
1848        The document is non-conforming.</p>
1849    
1850        <p>An entity labeled as Internet media type
1851        <code>text/cache-manifest</code> must contain a cache manifest.</p>
1852    
1853        <p>A cache manifest must start with a line whose content is
1854        <code class="manifest example">CACHE MANIFEST</code>
1855        (exactly one space character between
1856        <code>CACHE</code> and <code>MANIFEST</code>).</p>
1857      </div>
1858    
1859    <div class="section " id="same-as-manifest-URL"><h3>This URL is same as the manifest URL.</h3></div>
1860    
1861    </section>
1862    
1863    <section id="information">
1864    <h2>Stability Information</h2>
1865    
1866    <div class="section " id="deprecated:attr"><h3>This attribute is deprecated.</h3></div>
1867    
1868    <div class="section " id="deprecated:element"><h3>This element is deprecated.</h3></div>
1869    
1870    <div class="section " id="status:cr:element"><h3>This element is in the
1871      <strong>call for implementation</strong> stage.</h3>
1872        <p>The element is in the call for implementation stage.</p>
1873        
1874        <p>Usually, using the element is safe.  However, it is a new feature
1875        so that it might not be implemented correctly.  If it is found that
1876        the feature is hard or impossible to implement, the feature
1877        might be revised, or in some case it might be dropped.</p>
1878    
1879        <p>Elements defined by Atom 1.0 (IETF Proposed Standard), and XBL 2.0
1880        (W3C Candidate Recommendation) belong to this class.</p>
1881      </div>
1882    
1883    <div class="section " id="status:lc:element"><h3>This element is in the <strong>last
1884      call for comments</strong> stage.</h3>
1885        <p>The element is in the last call for comments stage.</p>
1886        
1887        <p>The element is relatively mature, though the standardization
1888        is not done yet.  It may be used for experiments.  Since it is a new
1889        feature, it might not be implemented correctly or at all.  If it is
1890        found that the feature is hard or impossible to implement, the feature
1891        might be revised or might be dropped.</p>
1892    
1893        <p>Elements defined by Web Forms 2.0 as well as some elements
1894        defined by HTML5 belong to this class.</p>
1895      </div>
1896    
1897    <div class="section " id="status:wd:element"><h3>This element is documented in a <strong>working
1898      draft</strong>.</h3>
1899        <p>The element is documented in a working or editor's draft
1900        and not yet completed.</p>
1901        
1902        <p>The element should not be used for any practical purpose.
1903        The feature might be drastically changed later or might be
1904        entirely removed.</p>
1905    
1906        <p>Most of new elements defined by HTML5 belong to this class.</p>
1907      </div>
1908    
1909    <div class="section " id="status:non-standard:element"><h3>This element is <strong>not part of any
1910      standard</strong> the conformance checker knows.</h3>
1911        <p>The element is not part of any standard or draft the conformance
1912        checker is aware of.</p>
1913        
1914        <p>The element should not be used for any practical purpose unless
1915        there is really a standard that defines the element.</p>
1916      </div>
1917    
1918    <div class="section " id="status:cr:attr"><h3>This attribute is in the
1919      <strong>call for implementation</strong> stage.</h3>
1920        <p>The attribute is in the call for implementation stage.</p>
1921        
1922        <p>Usually, using the attribute is safe.  However, it is a new feature
1923        so that it might not be implemented correctly.  If it is found that
1924        the feature is hard or impossible to implement, the feature
1925        might be revised, or in some case it might be dropped.</p>
1926      </div>
1927    
1928    <div class="section " id="status:lc:attr"><h3>This attribute is in the <strong>last
1929      call for comments</strong> stage.</h3>
1930        <p>The attribute is in the last call for comments stage.</p>
1931        
1932        <p>The attribute is relatively mature, though the standardization
1933        is not done yet.  It may be used for experiments.  Since it is a new
1934        feature, it might not be implemented correctly or at all.  If it is
1935        found that the feature is hard or impossible to implement, the feature
1936        might be revised or might be dropped.</p>
1937      </div>
1938    
1939    <div class="section " id="status:wd:attr"><h3>This attribute is documented in a <strong>working
1940      draft</strong>.</h3>
1941        <p>The attribute is documented in a working or editor's draft
1942        and not yet completed.</p>
1943        
1944        <p>The attribute should not be used for any practical purpose.
1945        The feature might be drastically changed later or might be
1946        entirely removed.</p>
1947      </div>
1948    
1949    <div class="section " id="status:non-standard:attr"><h3>This attribute is <strong>not part of any
1950      standard</strong> the conformance checker knows.</h3>
1951        <p>The attribute is not part of any standard or draft the conformance
1952        checker is aware of.</p>
1953        
1954        <p>The attribute should not be used for any practical purpose unless
1955        there is really a standard that defines the attribute.</p>
1956      </div>
1957    </section>
1958    
1959    <section id="langtag-errors">
1960    <h2>Language Tag Errors</h2>
1961    
1962    <div class="section " id="langtag:extension:duplication"><h3>There is another extension subtag
1963      <code><var>{value}</var></code>.</h3></div>
1964    
1965    <div class="section " id="langtag:illegal"><h3>Subtag <code><var>{value}</var></code> is
1966      syntactically invalid.</h3></div>
1967    
1968    <div class="section " id="langtag:language:case"><h3>It is a good practice to represent ISO 639-1
1969      language code <code><var>{value}</var></code> in lowercase.</h3></div>
1970    
1971  <div class="section should" id="s:URI::empty-path"><h3>This IRI should explicitly end with  <div class="section " id="langtag:language:mul"><h3>Langauge tag <code>mul</code> should not be
1972    <code>/</code>.</h3></div>    used.</h3></div>
1973    
1974    <div class="section " id="langtag:language:nosemantics"><h3>No semantics is defined for language subtag
1975      <code><var>{value}</var></code>.</h3></div>
1976    
1977    <div class="section " id="langtag:language:syntax"><h3>The language subtag <code><var>{value}</var></code>
1978      is syntactically invalid.</h3></div>
1979    
1980    <div class="section " id="langtag:language:und"><h3>Langauge tag <code>und</code> should not be
1981      used.</h3></div>
1982    
1983    <div class="section " id="langtag:private"><h3>It would be better if a private use language
1984      tag (<code><var>{value}</var></code>) is not used.</h3></div>
1985    
1986    <div class="section " id="langtag:privateuse:syntax"><h3>Private use subtag <code><var>{value}</var></code>
1987      is syntactically invalid.</h3></div>
1988    
1989    <div class="section " id="langtag:region:case"><h3>It is a good practice to represent ISO 3166
1990      country code <code><var>{value}</var></code> in uppercase.</h3></div>
1991    
1992    <div class="section " id="langtag:region:nosemantics"><h3>No semantics is defined for region subtag
1993      <code><var>{value}</var></code>.</h3></div>
1994    
1995    <div class="section " id="langtag:region:private"><h3>Use of private use country code
1996      <code><var>{value}</var></code> is not allowed.</h3></div>
1997    
1998    </section>
1999    
2000    <section id="rdfxml-errors">
2001    <h2>RDF/XML Errors</h2>
2002    
2003    <div class="section " id="bad-rdf-namespace"><h3>The namespace URI of an element that
2004      represents an RDF concept must be
2005      <code>http://www.w3.org/1999/02/22-rdf-syntax-ns#</code>.</h3></div>
2006    
2007    <div class="section " id="duplicate-rdf-id"><h3>The specified value is already used as an
2008      ID.</h3></div>
2009    
2010    <div class="section " id="duplicate-unqualified-attr"><h3>Both unqualified attribute and namespace‐qualified
2011      RDF attribute are specified, which is not allowed.</h3></div>
2012    
2013    <div class="section " id="parse-type-other"><h3>An invalid value is specified to
2014      the <code>parseType</code> attribute.</h3></div>
2015    
2016    <div class="section " id="second-node-element"><h3>There is another element, such that
2017      this element is not allowed.</h3></div>
2018    
2019    <div class="section " id="unqualified-attr"><h3>Unqualified attribute is not allowed.</h3></div>
2020    
2021    <div class="section " id="unqualified-rdf-attr"><h3>RDF attribute should be
2022      namespace‐qualified.</h3></div>
2023    
2024  </section>  </section>
2025    
2026  <section id="unsupported-messages">  <section id="unsupported-messages">
2027  <h2><i>Unsupported</i> Messages</h2>  <h2><i>Unsupported</i> Messages</h2>
2028    
2029  <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
2030    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
2031      <p>The conformant checker does not support the attribute.    might not be conforming</em>.</h3>
2032        <p>The conformant checker does not support the element.
2033      It cannot determine whether the document is conforming or not.</p>      It cannot determine whether the document is conforming or not.</p>
2034    </div>    </div>
2035    
2036  <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
2037    conformance checker; <em>it might or might not be conforming</em>.</h3>    <code><var>{local-name}</var></code> of element
2038      <p>The conformant checker does not support the element.    <code><var>{element-local-name}</var></code> is not supported;
2039      <em>it might or might not be conforming</em>.</h3>
2040        <p>The conformant checker does not support the attribute.
2041      It cannot determine whether the document is conforming or not.</p>      It cannot determine whether the document is conforming or not.</p>
2042    </div>    </div>
2043    
2044  <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
2045    or registered at the time of the release of the conformance checker;    standardized or registered at the time of the release of the conformance
2046    <em>it is non-conforming unless it has now been registered</em>.</h3>    checker; <em>it is non-conforming unless it now has been
2047      registered</em>.</h3>
2048      <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.
2049      Some common link types are defined in the HTML5 specification.      Some common link types are defined in the HTML5 specification.
2050      Additional link types can be registered to the WHATWG Wiki.      Additional link types can be registered to the WHATWG Wiki.
# Line 217  Web Document Conformance Checker (BETA)< Line 2055  Web Document Conformance Checker (BETA)<
2055      The link type might have been added to the registry since then.      The link type might have been added to the registry since then.
2056      In such case it might be conforming.  Otherwise, the      In such case it might be conforming.  Otherwise, the
2057      document is non-conforming.</p>      document is non-conforming.</p>
2058    
2059        <dl>
2060        <dt>Link types <code>shortcut icon</code></dt>
2061            <dd>Link type <code>shortcut</code> is not registered.
2062            Use only <code>icon</code> for linking to so-called favicon.</dd>
2063        </dl>
2064    </div>    </div>
2065    
2066    <div class="section " id="event-handler"><h3>Conformance checking for event handler attribute
2067      is not supported; <em>it might or might not be conforming.</em></h3></div>
2068    
2069    <div class="section " id="media-query"><h3>Conformance checking for media query
2070      is not supported; <em>it might or might not be conforming.</em></h3></div>
2071    
2072    <div class="section " id="addr-spec-not-supported"><h3>Conformance checking for an <code>addr-spec</code>
2073      is not supported; <em>it might or might not be conforming.</em></h3></div>
2074    
2075    <div class="section " id="XML-script-lang"><h3>Conformance checking for script
2076      language <code><var>{text}</var></code> is not supported;
2077      <em>it might or might not be conforming.</em></h3></div>
2078    
2079    <div class="section " id="XML-style-lang"><h3>Conformance checking for style
2080      language <code><var>{text}</var></code> is not supported;
2081      <em>it might or might not be conforming.</em></h3></div>
2082    
2083    <div class="section " id="atom|content-not-supported"><h3>Conformance checking for an Atom
2084      <code>content</code> element with <code>type</code>
2085      <code><var>{text}</var></code> is not supported.</h3></div>
2086    
2087  </section>  </section>
2088    
2089  <d:catalog>  
2090  manakaiCompatMode:quirks;;Quirks Mode  
2091  manakaiCompatMode:limited quirks;;Limited Quirks Mode  
2092  manakaiCompatMode:no quirks;;No Quirks Mode  
2093    
2094  manakaiIsHTML:1;;HTML Document  
2095  manakaiIsHTML:0;;XML Document  
2096  </d:catalog>  
2097    
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2300    
2301    
2302    
2303    
2304    
2305    
2306    
2307    <section id="levels">
2308    <h2>Error Levels</h2>
2309    
2310    <table id="levels-table">
2311    <thead>
2312    <tr><th scope="col">Level</th>
2313    <th scope="col">Conforming?</th>
2314    <th scope="col">Description</th>
2315    </tr>
2316    </thead>
2317    <tbody>
2318    <tr class="level-m" id="level-m">
2319    <th scope="row"><em class="rfc2119">MUST</em>‐level error</th>
2320    <td>Non‐conforming.</td>
2321    <td>A violation to a hard requirement of the specification.
2322    The document is non‐conforming.</td>
2323    </tr>
2324    <tr class="level-s" id="level-s">
2325    <th scope="row"><em class="rfc2119">SHOULD</em>‐level error</th>
2326    <td>Non‐conforming, but <em>in some case</em>
2327    conforming.</td>
2328    <td>A violation to a requirement of the specification.
2329    The violation might be legitimize in some case.  Otherwise,
2330    the document is non‐conforming.</td>
2331    </tr>
2332    <tr class="level-w" id="level-w">
2333    <th scope="row">Warning</th>
2334    <td>Conforming.</td>
2335    <td>A warning is an advice from the conformance checker to avoid
2336    to solve a problem in a confusing or possibly wrong way.
2337    It does not affect to the conformance of the document, and
2338    may sometimes be inappropriate.</td>
2339    </tr>
2340    <tr class="level-i" id="level-i">
2341    <th scope="row">Information</th>
2342    <td>Conforming.</td>
2343    <td>An informational message just provides an additional information
2344    on the feature used in the document or the status of the retrieval
2345    or so on.
2346    It does not affect to the conformance of the document.</td>
2347    </tr>
2348    <tr class="level-u" id="level-u">
2349    <th scope="row">Not supported</th>
2350    <td><em>Unknown</em>.</td>
2351    <td>Some feature that is not supported by the conformance checker
2352    is used in the document.</td>
2353    </tr>
2354    </tbody>
2355    </table>
2356    </section>
2357    
2358  <section id="license">  <section id="license">
2359  <h2>License of This Document</h2>  <h2>License of This Document</h2>
2360    
2361  <p>Copyright 2007 <a href="http://suika.fam.cx/~wakaba/who?">Wakaba</a></p>  <p>Copyright <time>2007</time>‐<time>2008</time>
2362  <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>
2363    <code class="mail">&lt;<a href="mailto:[email protected]">[email protected]</a>&gt;</code>.</p>
2364    
2365    <p>This document is free software; you can redistribute it
2366  and/or modify it under the same terms as Perl itself.</p>  and/or modify it under the same terms as Perl itself.</p>
2367  </section>  </section>
2368    

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