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class="firstHeading mw-first-heading"><span class="mw-page-title-main">W3C Markup Validation Service</span></h1> <div id="p-lang-btn" class="vector-dropdown mw-portlet mw-portlet-lang" > <input type="checkbox" id="p-lang-btn-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-p-lang-btn" class="vector-dropdown-checkbox mw-interlanguage-selector" aria-label="Go to an article in another language. Available in 12 languages" > <label id="p-lang-btn-label" for="p-lang-btn-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--action-progressive mw-portlet-lang-heading-12" aria-hidden="true" ><span class="vector-icon mw-ui-icon-language-progressive mw-ui-icon-wikimedia-language-progressive"></span> <span class="vector-dropdown-label-text">12 languages</span> </label> <div class="vector-dropdown-content"> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li class="interlanguage-link interwiki-ca mw-list-item"><a href="https://ca.wikipedia.org/wiki/W3C_Markup_Validation_Service" title="W3C Markup Validation Service – Catalan" lang="ca" hreflang="ca" data-title="W3C Markup Validation Service" data-language-autonym="Català" data-language-local-name="Catalan" class="interlanguage-link-target"><span>Català</span></a></li><li class="interlanguage-link interwiki-da mw-list-item"><a href="https://da.wikipedia.org/wiki/Markup_Validation_Service" title="Markup Validation Service – Danish" lang="da" hreflang="da" data-title="Markup Validation Service" data-language-autonym="Dansk" data-language-local-name="Danish" class="interlanguage-link-target"><span>Dansk</span></a></li><li class="interlanguage-link interwiki-de mw-list-item"><a href="https://de.wikipedia.org/wiki/W3C_Markup_Validation_Service" title="W3C Markup Validation Service – German" lang="de" hreflang="de" data-title="W3C Markup Validation Service" data-language-autonym="Deutsch" data-language-local-name="German" class="interlanguage-link-target"><span>Deutsch</span></a></li><li class="interlanguage-link interwiki-es mw-list-item"><a href="https://es.wikipedia.org/wiki/W3C_Markup_Validation_Service" title="W3C Markup Validation Service – Spanish" lang="es" hreflang="es" data-title="W3C Markup Validation Service" data-language-autonym="Español" data-language-local-name="Spanish" class="interlanguage-link-target"><span>Español</span></a></li><li class="interlanguage-link interwiki-ko mw-list-item"><a href="https://ko.wikipedia.org/wiki/W3C_Markup_Validation_Service" title="W3C Markup Validation Service – Korean" lang="ko" hreflang="ko" data-title="W3C Markup Validation Service" data-language-autonym="한국어" data-language-local-name="Korean" class="interlanguage-link-target"><span>한국어</span></a></li><li class="interlanguage-link interwiki-id mw-list-item"><a href="https://id.wikipedia.org/wiki/W3C_Markup_Validation_Service" title="W3C Markup Validation Service – Indonesian" lang="id" hreflang="id" data-title="W3C Markup Validation Service" data-language-autonym="Bahasa Indonesia" data-language-local-name="Indonesian" class="interlanguage-link-target"><span>Bahasa Indonesia</span></a></li><li class="interlanguage-link interwiki-it mw-list-item"><a href="https://it.wikipedia.org/wiki/W3C_Validator" title="W3C Validator – Italian" lang="it" hreflang="it" 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href="https://sr.wikipedia.org/wiki/W3C_Markup_Validation_Service" title="W3C Markup Validation Service – Serbian" lang="sr" hreflang="sr" data-title="W3C Markup Validation Service" data-language-autonym="Српски / srpski" data-language-local-name="Serbian" class="interlanguage-link-target"><span>Српски / srpski</span></a></li><li class="interlanguage-link interwiki-sv mw-list-item"><a href="https://sv.wikipedia.org/wiki/W3C_Markup_Validation_Service" title="W3C Markup Validation Service – Swedish" lang="sv" hreflang="sv" data-title="W3C Markup Validation Service" data-language-autonym="Svenska" data-language-local-name="Swedish" class="interlanguage-link-target"><span>Svenska</span></a></li><li class="interlanguage-link interwiki-zh mw-list-item"><a href="https://zh.wikipedia.org/wiki/W3C%E9%A9%97%E8%A8%BC%E6%9C%8D%E5%8B%99" title="W3C驗証服務 – Chinese" lang="zh" hreflang="zh" data-title="W3C驗証服務" data-language-autonym="中文" data-language-local-name="Chinese" 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.tmulti .tsingle{margin:1px;float:left}.mw-parser-output .tmulti .theader{clear:both;font-weight:bold;text-align:center;align-self:center;background-color:transparent;width:100%}.mw-parser-output .tmulti .thumbcaption{background-color:transparent}.mw-parser-output .tmulti .text-align-left{text-align:left}.mw-parser-output .tmulti .text-align-right{text-align:right}.mw-parser-output .tmulti .text-align-center{text-align:center}@media all and (max-width:720px){.mw-parser-output .tmulti .thumbinner{width:100%!important;box-sizing:border-box;max-width:none!important;align-items:center}.mw-parser-output .tmulti .trow{justify-content:center}.mw-parser-output .tmulti .tsingle{float:none!important;max-width:100%!important;box-sizing:border-box;text-align:center}.mw-parser-output .tmulti .tsingle .thumbcaption{text-align:left}.mw-parser-output .tmulti .trow>.thumbcaption{text-align:center}}@media screen{html.skin-theme-clientpref-night .mw-parser-output .tmulti .multiimageinner img{background-color:white}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .tmulti .multiimageinner img{background-color:white}}</style><div class="thumb tmulti tright"><div class="thumbinner multiimageinner" style="width:204px;max-width:204px"><div class="trow"><div class="tsingle" style="width:202px;max-width:202px"><div class="thumbimage"><span typeof="mw:File"><a href="/wiki/File:Valid_XHTML_1.0.svg" class="mw-file-description"><img alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/1/1f/Valid_XHTML_1.0.svg/200px-Valid_XHTML_1.0.svg.png" decoding="async" width="200" height="70" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/1/1f/Valid_XHTML_1.0.svg/300px-Valid_XHTML_1.0.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/1/1f/Valid_XHTML_1.0.svg/400px-Valid_XHTML_1.0.svg.png 2x" data-file-width="512" data-file-height="180" /></a></span></div></div></div><div class="trow"><div class="tsingle" style="width:202px;max-width:202px"><div class="thumbimage"><span typeof="mw:File"><a href="/wiki/File:Valid_CSS.svg" class="mw-file-description"><img alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/1/10/Valid_CSS.svg/200px-Valid_CSS.svg.png" decoding="async" width="200" height="70" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/1/10/Valid_CSS.svg/300px-Valid_CSS.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/1/10/Valid_CSS.svg/400px-Valid_CSS.svg.png 2x" data-file-width="512" data-file-height="180" /></a></span></div><div class="thumbcaption">Tag certifying that a website has been checked for well-formed XHTML (above) and CSS (below) markup</div></div></div></div></div> <p>The <b>Markup Validation Service</b> is a <a href="/wiki/Validator" title="Validator">validator</a> by the <a href="/wiki/World_Wide_Web_Consortium" title="World Wide Web Consortium">World Wide Web Consortium</a> (W3C) that allows <a href="/wiki/Internet" title="Internet">Internet</a> users to check pre-HTML5 <a href="/wiki/HTML" title="HTML">HTML</a> and <a href="/wiki/XHTML" title="XHTML">XHTML</a> documents for <a href="/wiki/Well-formed_element" title="Well-formed element">well-formed</a> markup against a <a href="/wiki/Document_type_definition" title="Document type definition">document type definition</a> (DTD). Markup validation is an important step towards ensuring the technical quality of web pages. However, it is not a complete measure of <a href="/wiki/Web_standards" title="Web standards">web standards</a> conformance.<sup id="cite_ref-w3.org_about_1-0" class="reference"><a href="#cite_note-w3.org_about-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> Though W3C validation is important for browser compatibility and site usability, it has not been confirmed what effect it has on <a href="/wiki/Search_engine_optimization" title="Search engine optimization">search engine optimization</a>. </p><p>As <a href="/wiki/HTML5" title="HTML5">HTML5</a> has removed the use of DTD in favor of a "Living Standard", the traditional Markup Validation Service is not applicable to these formats. Validation is instead performed using an open-source "Nu Validator", an instance of which is provided by W3C.<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> </p> <meta property="mw:PageProp/toc" /> <div class="mw-heading mw-heading2"><h2 id="History">History</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=W3C_Markup_Validation_Service&action=edit&section=1" title="Edit section: History"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The Markup Validation Service began as <i>The Kinder, Gentler HTML Validator</i>, a project by Gerald Oskoboiny.<sup id="cite_ref-w3.org_about_1-1" class="reference"><a href="#cite_note-w3.org_about-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> It was developed to be a more intuitive version of the first online HTML validator written by Dan Connolly and Mark Gaither, which was announced on July 13, 1994.<sup id="cite_ref-www-html_validator_3-0" class="reference"><a href="#cite_note-www-html_validator-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> </p><p>In September 1997, Oskoboiny began working for the W3C, and on December 18, 1997, the W3C announced its <i>W3C HTML Validator</i> based upon his works.<sup id="cite_ref-oskoboiny_kgv_4-0" class="reference"><a href="#cite_note-oskoboiny_kgv-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> In November 2008, the W3C released the validator.nu HTML5 engine and the ability to check documents for conformance to HTML5.<sup id="cite_ref-5" class="reference"><a href="#cite_note-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> </p><p>W3C also offers validation tools for web technologies other than HTML/XHTML, such as <a href="/wiki/CSS" title="CSS">CSS</a>, <a href="/wiki/XML_Schema_(W3C)" title="XML Schema (W3C)">XML schemas</a>, and <a href="/wiki/MathML" title="MathML">MathML</a>.<sup id="cite_ref-W3C_CSS_6-0" class="reference"><a href="#cite_note-W3C_CSS-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Browser_accommodation">Browser accommodation</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=W3C_Markup_Validation_Service&action=edit&section=2" title="Edit section: Browser accommodation"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Many major <a href="/wiki/Web_browsers" class="mw-redirect" title="Web browsers">web browsers</a> are often tolerant of certain types of error, and may display a document successfully even if it is not syntactically correct. Certain other <a href="/wiki/XML" title="XML">XML</a> documents can also be validated if they refer to an internal or external <a href="/wiki/Document_Type_Definition" class="mw-redirect" title="Document Type Definition">DTD</a>. </p> <div class="mw-heading mw-heading2"><h2 id="Limitations">Limitations</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=W3C_Markup_Validation_Service&action=edit&section=3" title="Edit section: Limitations"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Mark-up validators cannot see the "big picture" on a web page,<sup class="noprint Inline-Template" style="margin-left:0.1em; white-space:nowrap;">[<i><a href="/wiki/Wikipedia:Please_clarify" title="Wikipedia:Please clarify"><span title="The text near this tag may need clarification or removal of jargon. (September 2021)">clarification needed</span></a></i>]</sup> but they excel at picking up missed closing tags and other technicalities.<sup id="cite_ref-W3C_CSS_6-1" class="reference"><a href="#cite_note-W3C_CSS-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Castro_7-0" class="reference"><a href="#cite_note-Castro-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup> </p><p>DTD-based validators are also limited in their ability to check attribute values according to many specification documents. For example, using an HTML 4.01 DOCTYPE, <code>bgcolor="fffff"</code> is accepted as valid for the "body" element even though the value "fffff" is missing a preceding '#' character and contains only five (instead of six) hexadecimal digits. Also, for the "img" element, width="really wide" is also accepted as valid. DTD-based validators are technically not able to test for these types of attribute value problems. </p><p>Pages may not display as intended in all browsers, even in the absence of validation errors and successful display in other browsers. The only way to ensure that pages always display as intended is to test them in all browsers expected to render them correctly.<sup id="cite_ref-Castro_7-1" class="reference"><a href="#cite_note-Castro-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="CSS_validation">CSS validation</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=W3C_Markup_Validation_Service&action=edit&section=4" title="Edit section: CSS validation"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>While the W3C and other HTML and XHTML validators will assess pages coded in those formats, a separate validator like the W3C CSS validator can check that there are no errors in the associated <a href="/wiki/Cascading_Style_Sheet" class="mw-redirect" title="Cascading Style Sheet">Cascading Style Sheet</a>. CSS validators apply current CSS standards to referenced CSS documents.<sup id="cite_ref-Castro_7-2" class="reference"><a href="#cite_note-Castro-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=W3C_Markup_Validation_Service&action=edit&section=5" title="Edit section: See also"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a href="/wiki/HTML_Tidy" title="HTML Tidy">HTML Tidy</a>, an offline markup validation program developed by <a href="/wiki/Dave_Raggett" title="Dave Raggett">Dave Raggett</a> of <a href="/wiki/W3C" class="mw-redirect" title="W3C">W3C</a></li> <li><a href="/wiki/CSS_HTML_Validator" title="CSS HTML Validator">CSS HTML Validator</a>, offline <a href="/wiki/HTML" title="HTML">HTML</a> and <a href="/wiki/CSS" title="CSS">CSS</a> validator desktop software</li> <li><a href="/wiki/World_Wide_Web_Consortium" title="World Wide Web Consortium">World Wide Web Consortium</a> (W3C)</li></ul> <div class="mw-heading mw-heading2"><h2 id="References">References</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=W3C_Markup_Validation_Service&action=edit&section=6" title="Edit section: References"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1239543626">.mw-parser-output .reflist{margin-bottom:0.5em;list-style-type:decimal}@media screen{.mw-parser-output .reflist{font-size:90%}}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}</style><div class="reflist"> <div class="mw-references-wrap"><ol class="references"> <li id="cite_note-w3.org_about-1"><span class="mw-cite-backlink">^ <a href="#cite_ref-w3.org_about_1-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-w3.org_about_1-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><style data-mw-deduplicate="TemplateStyles:r1238218222">.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free.id-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/6/65/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited.id-lock-limited a,.mw-parser-output .id-lock-registration.id-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription.id-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-free a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-limited a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-registration a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-subscription a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .cs1-ws-icon a{background-size:contain;padding:0 1em 0 0}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:var(--color-error,#d33)}.mw-parser-output .cs1-visible-error{color:var(--color-error,#d33)}.mw-parser-output .cs1-maint{display:none;color:#085;margin-left:0.3em}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}@media screen{.mw-parser-output .cs1-format{font-size:95%}html.skin-theme-clientpref-night .mw-parser-output .cs1-maint{color:#18911f}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .cs1-maint{color:#18911f}}</style><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://validator.w3.org/about.html">"About the W3C Markup Validation Service"</a>. <i>W3C Markup Validation Service</i>. World Wide Web Consortium<span class="reference-accessdate">. Retrieved <span class="nowrap">2011-05-20</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=W3C+Markup+Validation+Service&rft.atitle=About+the+W3C+Markup+Validation+Service&rft_id=http%3A%2F%2Fvalidator.w3.org%2Fabout.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3AW3C+Markup+Validation+Service" class="Z3988"></span></span> </li> <li id="cite_note-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-2">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://validator.w3.org/nu/">"Ready to check - Nu Html Checker"</a>. <i>validator.w3.org</i>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=validator.w3.org&rft.atitle=Ready+to+check+-+Nu+Html+Checker&rft_id=https%3A%2F%2Fvalidator.w3.org%2Fnu%2F&rfr_id=info%3Asid%2Fen.wikipedia.org%3AW3C+Markup+Validation+Service" class="Z3988"></span></span> </li> <li id="cite_note-www-html_validator-3"><span class="mw-cite-backlink"><b><a href="#cite_ref-www-html_validator_3-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFConnolly1994" class="citation mailinglist cs1">Connolly, Dan (1994-07-13). <a rel="nofollow" class="external text" href="//lists.w3.org/Archives/Public/www-html/1994Jul/0015">"ANNOUNCE: HaL Interactive HTML Validation Service"</a>. <i>www-html</i> (Mailing list)<span class="reference-accessdate">. Retrieved <span class="nowrap">2008-06-28</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=ANNOUNCE%3A+HaL+Interactive+HTML+Validation+Service&rft.date=1994-07-13&rft.aulast=Connolly&rft.aufirst=Dan&rft_id=%2F%2Flists.w3.org%2FArchives%2FPublic%2Fwww-html%2F1994Jul%2F0015&rfr_id=info%3Asid%2Fen.wikipedia.org%3AW3C+Markup+Validation+Service" class="Z3988"></span></span> </li> <li id="cite_note-oskoboiny_kgv-4"><span class="mw-cite-backlink"><b><a href="#cite_ref-oskoboiny_kgv_4-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFOskoboiny2003" class="citation web cs1">Oskoboiny, Gerald (2003-03-22). <a rel="nofollow" class="external text" href="http://impressive.net/people/gerald/1996/ugweb/validate/changes.html">"History of the Kinder, Gentler HTML Validator"</a><span class="reference-accessdate">. Retrieved <span class="nowrap">2008-06-28</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=History+of+the+Kinder%2C+Gentler+HTML+Validator&rft.date=2003-03-22&rft.aulast=Oskoboiny&rft.aufirst=Gerald&rft_id=http%3A%2F%2Fimpressive.net%2Fpeople%2Fgerald%2F1996%2Fugweb%2Fvalidate%2Fchanges.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3AW3C+Markup+Validation+Service" class="Z3988"></span></span> </li> <li id="cite_note-5"><span class="mw-cite-backlink"><b><a href="#cite_ref-5">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://validator.w3.org/whatsnew.html">"What's New at The W3C Markup Validation Service"</a>. <i>validator.w3.org</i><span class="reference-accessdate">. Retrieved <span class="nowrap">2016-05-31</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=validator.w3.org&rft.atitle=What%27s+New+at+The+W3C+Markup+Validation+Service&rft_id=https%3A%2F%2Fvalidator.w3.org%2Fwhatsnew.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3AW3C+Markup+Validation+Service" class="Z3988"></span></span> </li> <li id="cite_note-W3C_CSS-6"><span class="mw-cite-backlink">^ <a href="#cite_ref-W3C_CSS_6-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-W3C_CSS_6-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://jigsaw.w3.org/css-validator/about.html">"About the CSS Validator"</a>. World Wide Web Consortium<span class="reference-accessdate">. Retrieved <span class="nowrap">2012-06-24</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=About+the+CSS+Validator&rft.pub=World+Wide+Web+Consortium&rft_id=http%3A%2F%2Fjigsaw.w3.org%2Fcss-validator%2Fabout.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3AW3C+Markup+Validation+Service" class="Z3988"></span></span> </li> <li id="cite_note-Castro-7"><span class="mw-cite-backlink">^ <a href="#cite_ref-Castro_7-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-Castro_7-1"><sup><i><b>b</b></i></sup></a> <a href="#cite_ref-Castro_7-2"><sup><i><b>c</b></i></sup></a></span> <span class="reference-text">Castro, Elisabeth: <i>HTML, XHTML & CSS, Sixth Edition</i>, page 345–346. Visual Quickstart Guides, Peachpit Press, 2007. <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/0-321-43084-0" title="Special:BookSources/0-321-43084-0">0-321-43084-0</a></span> </li> </ol></div></div> <div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=W3C_Markup_Validation_Service&action=edit&section=7" title="Edit section: External links"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1235681985">.mw-parser-output .side-box{margin:4px 0;box-sizing:border-box;border:1px solid #aaa;font-size:88%;line-height:1.25em;background-color:var(--background-color-interactive-subtle,#f8f9fa);display:flow-root}.mw-parser-output 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style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/ActivityPub" title="ActivityPub">ActivityPub</a></li> <li><a href="/wiki/Activity_Streams_(format)" title="Activity Streams (format)">Activity Streams</a></li> <li><a href="/wiki/WAI-ARIA" title="WAI-ARIA">ARIA</a></li> <li><a href="/wiki/Canonical_XML" title="Canonical XML">Canonical XML</a></li> <li><a href="/wiki/Compound_Document_Format" title="Compound Document Format">CDF</a></li> <li><a href="/wiki/CSS" title="CSS">CSS</a> <ul><li><a href="/wiki/CSS_animations" title="CSS animations">Animations</a></li> <li><a href="/wiki/CSS_Flexible_Box_Layout" title="CSS Flexible Box Layout">Flexbox</a></li> <li><a href="/wiki/CSS_grid_layout" title="CSS grid layout">Grid</a></li></ul></li> <li><a href="/wiki/Document_Object_Model" title="Document Object Model">DOM</a></li> <li><a href="/wiki/Efficient_XML_Interchange" title="Efficient XML Interchange">EXI</a></li> <li><a href="/wiki/Emotion_Markup_Language" title="Emotion Markup Language">EmotionML</a></li> <li><a href="/wiki/W3C_Geolocation_API" title="W3C Geolocation API">Geolocation API</a></li> <li><a href="/wiki/HTML" title="HTML">HTML</a> <ul><li><a href="/wiki/HTML5" title="HTML5">HTML5</a></li></ul></li> <li><a href="/wiki/Indexed_Database_API" title="Indexed Database API">IndexedDB</a></li> <li><a href="/wiki/Internationalization_Tag_Set" title="Internationalization Tag Set">ITS</a></li> <li><a href="/wiki/JSON-LD" title="JSON-LD">JSON-LD</a></li> <li><a href="/wiki/Linked_Data_Notifications" title="Linked Data Notifications">Linked Data Notifications</a></li> <li><a href="/wiki/MathML" title="MathML">MathML</a></li> <li><a href="/wiki/Micropub_(protocol)" title="Micropub (protocol)">Micropub</a></li> <li><a href="/wiki/Web_Ontology_Language" title="Web Ontology Language">OWL</a></li> <li><a href="/wiki/Pronunciation_Lexicon_Specification" title="Pronunciation Lexicon Specification">PLS</a></li> <li><a href="/wiki/Resource_Description_Framework" title="Resource Description Framework">RDF</a> <ul><li><a href="/wiki/RDF_Schema" title="RDF Schema">Schema</a></li></ul></li> <li><a href="/wiki/Semantic_Interpretation_for_Speech_Recognition" title="Semantic Interpretation for Speech Recognition">SISR</a></li> <li><a href="/wiki/Simple_Knowledge_Organization_System" title="Simple Knowledge Organization System">SKOS</a></li> <li><a href="/wiki/Synchronized_Multimedia_Integration_Language" title="Synchronized Multimedia Integration Language">SMIL</a></li> <li><a href="/wiki/SOAP" title="SOAP">SOAP</a></li> <li><a href="/wiki/Speech_Recognition_Grammar_Specification" title="Speech Recognition Grammar Specification">SRGS</a></li> <li><a href="/wiki/Subresource_Integrity" title="Subresource Integrity">SRI</a></li> <li><a href="/wiki/Speech_Synthesis_Markup_Language" title="Speech Synthesis Markup Language">SSML</a></li> <li><a href="/wiki/Scalable_Vector_Graphics" class="mw-redirect" title="Scalable Vector Graphics">SVG</a> <ul><li><a href="/wiki/SVG_filter_effects" title="SVG filter effects">Filter Effects</a></li></ul></li> <li><a href="/wiki/SCXML" title="SCXML">SCXML</a></li> <li><a href="/wiki/SHACL" title="SHACL">SHACL</a></li> <li><a href="/wiki/SPARQL" title="SPARQL">SPARQL</a></li> <li><a href="/wiki/Timed_text" title="Timed text">Timed text</a></li> <li><a href="/wiki/VoiceXML" title="VoiceXML">VoiceXML</a></li> <li><a href="/wiki/WebAssembly" title="WebAssembly">WebAssembly</a></li> <li><a href="/wiki/Web_of_Things" title="Web of Things">WoT</a> <ul><li><a href="/wiki/Thing_Description" title="Thing Description">TD</a></li></ul></li> <li><a href="/wiki/Web_storage" title="Web storage">Web storage</a></li> <li><a href="/wiki/Web_Services_Description_Language" title="Web Services Description Language">WSDL</a></li> <li><a href="/wiki/Webmention" title="Webmention">Webmention</a></li> <li><a href="/wiki/WebSub" title="WebSub">WebSub</a></li> <li><a href="/wiki/WebVTT" title="WebVTT">WebVTT</a></li> <li><a href="/wiki/Web_Open_Font_Format" title="Web Open Font Format">WOFF</a></li> <li><a href="/wiki/XHTML" title="XHTML">XHTML</a> <ul><li><a href="/wiki/XHTML%2BRDFa" title="XHTML+RDFa">+RDFa</a></li></ul></li> <li><a href="/wiki/XML" title="XML">XML</a> <ul><li><a href="/wiki/XML_Base" title="XML Base">Base</a></li> <li><a href="/wiki/XML_Encryption" title="XML Encryption">Encryption</a></li> <li><a href="/wiki/XML_Events" title="XML Events">Events</a></li> <li><a href="/wiki/XML_Information_Set" title="XML Information Set">Information Set</a></li> <li><a href="/wiki/XML_namespace" title="XML namespace">Namespace</a></li> <li><a href="/wiki/XML_Schema_(W3C)" title="XML Schema (W3C)">Schema</a></li> <li><a href="/wiki/XML_Signature" title="XML Signature">Signature</a></li> <li><a href="/wiki/XForms" title="XForms">XForms</a></li> <li><a href="/wiki/XInclude" title="XInclude">XInclude</a></li> <li><a href="/wiki/XLink" title="XLink">XLink</a></li> <li><a href="/wiki/XML-binary_Optimized_Packaging" title="XML-binary Optimized Packaging">XOP</a></li> <li><a href="/wiki/XPath" title="XPath">XPath</a> <ul><li><a href="/wiki/XPath_2.0" title="XPath 2.0">2.0</a></li> <li><a href="/wiki/XPath_3" title="XPath 3">3.x</a></li></ul></li> <li><a href="/wiki/XPointer" title="XPointer">XPointer</a></li> <li><a href="/wiki/XProc" title="XProc">XProc</a></li> <li><a href="/wiki/XQuery" title="XQuery">XQuery</a></li> <li><a href="/wiki/XSL" title="XSL">XSL</a></li> <li><a href="/wiki/XSL_Formatting_Objects" title="XSL Formatting Objects">XSL-FO</a></li> <li><a href="/wiki/XSLT" title="XSLT">XSLT</a> <ul><li><a href="/wiki/XSLT_elements" title="XSLT elements">elements</a></li></ul></li></ul></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Notes</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/IndieAuth" title="IndieAuth">IndieAuth</a></li> <li><a href="/wiki/XAdES" title="XAdES">XAdES</a></li> <li><a href="/wiki/XBL" title="XBL">XBL</a></li> <li><a href="/wiki/XHTML%2BSMIL" title="XHTML+SMIL">XHTML+SMIL</a></li> <li><a href="/wiki/Extensible_User_Interface_Protocol" title="Extensible User Interface Protocol">XUP</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/World_Wide_Web_Consortium#Working_draft_(WD)" title="World Wide Web Consortium">Working drafts</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Call_Control_eXtensible_Markup_Language" title="Call Control eXtensible Markup Language">CCXML</a></li> <li><a href="/wiki/CURIE" title="CURIE">CURIE</a></li> <li><a href="/wiki/Encrypted_Media_Extensions" title="Encrypted Media Extensions">EME</a></li> <li><a href="/wiki/InkML" title="InkML">InkML</a></li> <li><a href="/wiki/Media_Source_Extensions" title="Media Source Extensions">MSE</a></li> <li><a href="/wiki/Rule_Interchange_Format" title="Rule Interchange Format">RIF</a></li> <li><a href="/wiki/SMIL_Timesheets" title="SMIL Timesheets">SMIL Timesheets</a></li> <li><a href="/wiki/SXBL" title="SXBL">sXBL</a></li> <li><a href="/wiki/WebGPU" title="WebGPU">WebGPU</a></li> <li><a href="/wiki/WebXR" title="WebXR">WebXR</a></li> <li><a href="/wiki/Extensible_Forms_Description_Language" title="Extensible Forms Description Language">XFDL</a></li> <li><a href="/wiki/XFrames" title="XFrames">XFrames</a></li> <li><a href="/wiki/XMLHttpRequest" title="XMLHttpRequest">XMLHttpRequest</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Guidelines</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Web_Content_Accessibility_Guidelines" title="Web Content Accessibility Guidelines">Web Content Accessibility Guidelines</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Initiative</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a class="mw-selflink selflink">Markup Validation Service</a></li> <li><a href="/wiki/Web_Accessibility_Initiative" title="Web Accessibility Initiative">Web Accessibility Initiative</a></li> <li><a href="/wiki/Web_Components" title="Web Components">Web Components</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Deprecated</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/C-HTML" class="mw-redirect" title="C-HTML">C-HTML</a></li> <li><a href="/wiki/Handheld_Device_Markup_Language" title="Handheld Device Markup Language">HDML</a></li> <li><a href="/wiki/JavaScript_Style_Sheets" title="JavaScript Style Sheets">JSSS</a></li> <li><a href="/wiki/Precision_Graphics_Markup_Language" title="Precision Graphics Markup Language">PGML</a></li> <li><a href="/wiki/Vector_Markup_Language" title="Vector Markup Language">VML</a></li> <li><a href="/wiki/WebPlatform.org" title="WebPlatform.org">WebPlatform</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Obsoleted</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/P3P" title="P3P">P3P</a></li> <li><a href="/wiki/XHTML%2BMathML%2BSVG" title="XHTML+MathML+SVG">XHTML+MathML+SVG</a></li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Organizations</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><td colspan="2" class="navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/World_Wide_Web_Foundation" title="World Wide Web Foundation">World Wide Web Foundation</a></li> <li><a href="/wiki/WHATWG" title="WHATWG">WHATWG</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Elected groups</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/w/index.php?title=W3C_Advisory_Board&action=edit&redlink=1" class="new" title="W3C Advisory Board (page does not exist)">AB</a></li> <li><a href="/w/index.php?title=W3C_Board&action=edit&redlink=1" class="new" title="W3C Board (page does not exist)">Board</a></li> <li><a href="/wiki/Technical_Architecture_Group" title="Technical Architecture Group">TAG</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Working groups</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/CSS_Working_Group" title="CSS Working Group">CSS</a></li> <li><a href="/wiki/SVG_Working_Group" title="SVG Working Group">SVG</a></li> <li><a href="/wiki/WebAssembly" title="WebAssembly">WebAssembly</a></li> <li><a href="/wiki/Web_Authentication_Working_Group" title="Web Authentication Working Group">WebAuthn</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Community & business groups</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Improving_Web_Advertising_Business_Group" title="Improving Web Advertising Business Group">Web Advertising BG</a></li> <li><a href="/wiki/WebAssembly" title="WebAssembly">WebAssembly</a> CG</li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Closed groups</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/W3C_Device_Description_Working_Group" title="W3C Device Description Working Group">Device Description</a> (DDWG)</li> <li><a href="/wiki/HTML_Working_Group" title="HTML Working Group">HTML</a></li> <li><a href="/wiki/W3C_MMI" title="W3C MMI">Multimodal Interaction Activity</a> (MMI)</li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Software</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><td colspan="2" class="navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/CERN_httpd" title="CERN httpd">CERN httpd</a></li> <li><a href="/wiki/Libwww" title="Libwww">Libwww</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Web_browser" title="Web browser">Browsers</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Line_Mode_Browser" title="Line Mode Browser">Line Mode</a> <span style="font-size:85%;">(1990–)</span></li> <li><a href="/wiki/Arena_(web_browser)" title="Arena (web browser)">Arena</a> <span style="font-size:85%;">(1993–98)</span></li> <li><a href="/wiki/Agora_(web_browser)" title="Agora (web browser)">Agora</a> <span style="font-size:85%;">(1994–97)</span></li> <li><a href="/wiki/Argo_(web_browser)" title="Argo (web browser)">Argo</a> <span style="font-size:85%;">(1994–97)</span></li> <li><a href="/wiki/Amaya_(web_editor)" title="Amaya (web editor)">Amaya</a> <span style="font-size:85%;">(browser/editor, 1996–2012)</span></li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Conferences</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/International_World_Wide_Web_Conference" class="mw-redirect" title="International World Wide Web Conference">International World Wide Web Conference</a> (IW3C) <ul><li><a href="/wiki/International_World_Wide_Web_Conferences_Steering_Committee" class="mw-redirect" title="International World Wide Web Conferences Steering Committee">Steering Committee</a> (IW3C2)</li> <li><a href="/wiki/First_International_Conference_on_the_World-Wide_Web" title="First International Conference on the World-Wide Web">First conference</a> ("WWW1", 1994)</li></ul></li></ul> </div></td></tr></tbody></table></div>    </div><noscript><img src="https://login.wikimedia.org/wiki/Special:CentralAutoLogin/start?type=1x1" alt="" width="1" 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