path: root/htdocs/docs/help.html

<!--#set var="revision" value="\$Id: help.html,v 1.21 2005-01-19 08:16:48 ot Exp $"
--><!--#set var="date" value="\$Date: 2005-01-19 08:16:48 $"
--><!--#set var="title" value="Help for The W3C Markup Validation Service"
--><!--#set var="relroot" value="../"
--><!--#include virtual="../header.html" -->

<div class="doc">
<h2>Help and <acronym title="Frequently Asked Questions">FAQ</acronym> for the Markup Validator</h2>

<p><q cite="http://lists.w3.org/Archives/Public/www-validator/2004Jan/0101.html">Nothing wrong with 
the validator here, it just knows HTML better than you do.</q> -- David Dorward, Validator's 
mailing-list.</p>

<h3 id="TableOfContents">Table of contents</h3>
<div id="toc">
<ol>
  <li>About the Markup Validator
  <ol>
        <li>
		<a href="#clickedandlost">Help me! I clicked on an icon and ended up 
		on this strange site!</a>
	</li>
	<li>
		<a href="#validation_basics">What is <em>Markup Validation</em>?</a>
	</li>
	<li>
		<a href="#validandquality">Is validation some kind of quality control? 
	Does "valid" mean "quality approved by W3C"?</a>
	</li>
	<li>
		<strong><a href="#what-is-it">What is the Markup Validator and what does it do?</a></strong>
	</li>
	<li>
		<a href="#why-validate">Why validate?</a>
	</li>
	<li>
		<a href="#who-does-validator">Who owns/maintain the Markup Validator?</a>
	</li>
	<li>
		<a href="#others">What other validators are there?</a>
	</li>
	<li>
		<a href="#how">How does The Validator work?</a>
	</li>
	<li>
		<a href="#howto-feedback">How do I send feedback/bug reports 
		about the Markup Validator?</a>
	</li>
  </ol>
  </li>
  <li>Using this service
  <ol>
	<li>
		<strong><a href="#manual">How do I use the Markup validator?</a></strong>
	</li>	
	<li>
		<a href="#errors">What is (are) this (these) error message(s)?</a>
	</li>	
	<li>
		<a href="#munged-doctype">Many error messages? Don't panic.</a>
	</li>
	<li>
		<a href="#cleanup">I don't want error messages, I want you to clean up my page!</a>
	</li>
	<li>
		<a href="#icon">My document is valid, can I use your "valid" icon?</a>
	</li>
  </ol>
  </li>
  <li>Miscellaneous (Very) Frequently Asked Questions
  <ol>
	<li>
		<a href="#faq-doctype"><q>No DOCTYPE Declaration Found!</q></a>
	</li>
	<li>
		<a href="#faq-charset"><q>No Character Encoding Found!</q></a> 
	</li>
	<li>
		<a href="#faq-ampersand">The validator complains about "&amp;" in my URLs!</a>
	</li>
	<li>
		<a href="#faq-javascript">The validator complains about something in my JavaScript!</a>
	</li>
	<li>
		<a href="#faq-linkandmeta">Why doesn't the validator like my &lt;link ... /&gt; 
		or &lt;meta ... /&gt;?</a>
	</li>
	<li>
		<a href="#faq-typo">I found some nasty typo like &lt;p&lt;a ...&gt; 
		and the validator accepted it!</a>
	</li>
	<li>
		<a href="#faq-referer">/check/referer does not work</a> or the validator says it does not support 
		my <a href="#faq-referer">"undefined" URL scheme</a>
	</li>
   </ol>
   </li>
</ol>
</div>


<div><a id="skip" name="skip"></a>
<h3 id="about">About the Markup Validator</h3>
    <h4 id="clickedandlost">Help me! I clicked on an icon and ended up on this strange site!</h4>
      <p>Don't panic!</p>

      <p>
	The author of the Web page you come from once used our service
	to <em>validate</em> that page, and the page passed validation. 
	The author was then authorized to use the icon on that page, as
	a claim of <em>validity</em>. The icon is used as a link back to
	the validation service, so that the author can <em>revalidate</em>
	whenever necessary. This is why, by clicking on the icon, you 
	followed a link to the current <em>validation results</em> for
	the page you came from.
      </p>

      <p>
	The validation result was certainly positive ("this page is valid..."),
	but if it wasn't, you would probably do the author of the page where
	the icon was a favor if you could warn him/her of this abnormal situation.
      </p>


      <p>
	If you are curious about Markup validation you may read this
	help document further, or you may simply use the back button
	of your Web browser to come back to the page where you found 
	the "valid" icon.
      </p>

    <h4 id="validation_basics">What is <em>Markup Validation</em>?</h4>
      <p>Most pages on the World Wide Web are written in computer languages
	(such as <acronym title="HyperText Markup Language">HTML</acronym>)
	that allow Web authors to structure text, add multimedia content, and
	specify what appearance, or style, the result should have.</p>

     <p>As for every language, these have their own <em>grammar</em>, <em>vocabulary</em>
	and <em>syntax</em>, and every document written with these computer languages
	are supposed to follow these rules. However, just as texts in a natural language
	can include spelling or grammar errors, documents using Markup  languages
	may (for various reasons) not be following these rules.</p>

      <p>The process of verifying whether a document actually follows the rules for the
	language(s) it uses is called <em>validation</em>, and the tool used for that
	is a validator. A document that passes this process with success is called 
	<em>valid</em>.
      </p>

    <h4 id="validandquality">Is validation some kind of quality control? 
	Does "valid" mean "quality approved by W3C"?</h4>

      <p>Validity is one of the quality criteria for a Web page, but there are
	many others. In other words, a <em>valid</em> Web page is not necessarily
	a good web page, but an <em>invalid</em> Web page has little chance
	of being a good web page.</p>

     <p>For that reason, the fact that the W3C Markup Validator says that
	one page passes validation does <strong>not</strong> mean that
	W3C assesses that it is a good page. It only means that a tool (not 
	necessarily without flaws) has found the page to comply with a specific
	set of rules. No more, no less. This is also why the "valid ..." icons 
	should never be considered as a "W3C seal of quality".</p>


    <h4 id="what-is-it">What is the Markup Validator and what does it do?</h4>
      <p>
	The Markup Validator is a free tool and service that checks the 
	syntax of (X)HTML documents.</p> 
      <p>
	The Validator is sort of like <code>lint</code> for C. It compares
        your HTML document to the defined syntax of HTML and reports any
        discrepancies. 
      </p>
      <p><a href="../about.html">Learn more</a> about the Markup Validator.</p>

    <h4 id="why-validate">Why should I validate my HTML pages?</h4>
      <p>
        One of the important maxims of computer programming is: <q>Be
        conservative in what you produce; be liberal in what you accept.</q>
      </p>
      <p>
        Browsers follow the second half of this maxim by accepting Web pages
        and trying to display them even if they're not legal HTML. Usually
        this means that the browser will try to make educated guesses about
        what you probably meant. The problem is that different browsers (or
        even different versions of the same browser) will make different
        guesses about the same illegal construct; worse, if your HTML is
        <em>really</em> pathological, the browser could get hopelessly
        confused and produce a mangled mess, or even crash.
      </p>
      <p>
        That's why you want to follow the first half of the maxim by making
        sure your pages are legal HTML. The best way to do that is by
        running your documents through one or more HTML validators. 
      </p>
      <p>A <a href="why.html">lengthier answer</a> to this question is
	also available on this site if the explanation above did not satisfy 
	you.
      </p>

    <h4 id="who-does-validator">Who owns/maintain the Markup Validator?</h4>
      <p>The Markup Validator is maintained at <acronym
	title="World Wide Web Consortium">W3C</acronym> by W3C staff and 
	benevolent collaborators, who receive a lot of help from contributors
	(read the <a href="../about.html#credits">full credits</a>).
      </p>

    <h4 id="others">What other validators are there?</h4>
	<p>
	We're doing our best to provide clear and reliable results as well as
	a good interface with the Markup Validator, but for some reason you
	may want to check other validators. Here are a few choices:
	</p>
	<ul>
	<li><a href="http://valet.webthing.com/page/">Page Valet</a>, part of the
	<a href="http://valet.webthing.com/">Site Valet</a> suite.</li>
	<li><a href="http://www.htmlhelp.com/tools/validator/">WDG's HTML validator</a></li>
	</ul>

	<p>
	Looking for validators at W3C, but not the Markup Validator?
	Check out the list of <a href="http://www.w3.org/QA/Tools/#validators">validators at W3C</a>,
	including well-known <a href="http://jigsaw.w3.org/css-validator/">CSS validator</a>,
	<a href="http://validator.w3.org/checklink">link checker</a>, etc.
	</p>
	

    <h4 id="how">How does The Validator work?</h4>
      <p>
	The Validator is based on <a href="http://www.jclark.com/">James
        Clark</a>'s <code><a href="http://www.jclark.com/sp/">nsgmls</a></code>
        SGML parser. The Validator itself is a CGI script that fetches your
        URL, passes it through <code>nsgmls</code>, and post-processes the
        resulting error list for easier reading. 
      </p>

    <h4 id="howto-feedback">How do I send feedback/bug reports about the Markup Validator?</h4>
      <p>Read the instructions on our <a href="../feedback.html">Feedback page</a>.</p>
</div>




<div>
<h3 id="using">Using this service</h3>

    <h4 id="manual">How do I use this service?</h4>
      <p>Most probably, you will want to use the online Markup Validation service.
	The simple way to use this service to validate a Web page is to paste its 
	address into the <a href="../#uri">text area</a> on the 
	<a href="..">validator's home page</a>, and press the "Check" button.</p>
      <p>There are other possible uses and a few usage options, please
	read the <a href="users.html">user's manual</a> for further help with this
	service.
      </p>
      <p>
	If, for some reason, you prefer running your own instance of the Markup Validator,
	check out our <a href="devel.html">developer's documentation</a>.
      </p>

    <h4 id="errors">What are these error messages?</h4>
      <p>The output of the Markup Validator may be hard to decipher for
	newcomers and experts alike, so we are maintaining a <a 
	href="errors.html">list of error
	messages and their interpretation</a>, which should help.
     </p>

    <h4 id="munged-doctype">Many error messages? Don't panic.</h4>
      <p>
        Don't panic. Did The Validator complain about your
        <code>DOCTYPE</code> declaration (or lack thereof)? Make sure your
        document has a syntactically correct <code>DOCTYPE</code>
        declaration, as described in the <a href="sgml.html#doctype">section
        on <code>DOCTYPE</code></a>, and make sure it correctly identifies
        the type of HTML you're using. Then run it through The Validator
        again; if you're lucky, you should get a lot fewer errors.
      </p>
      <p>
        If this doesn't help, then you may be experiencing a cascade failure
        &mdash; one error that gets The Validator so confused that it can't
        make sense of the rest of your page. Try correcting the first few
        errors and running your page through The Validator again. 
      </p>
      <p>
	Be patient, with a little time and experience you will learn to use the 
	Markup Validator to clean up your HTML documents in no time.
      </p>

    <h4 id="cleanup">I don't want error messages, I want you to clean up my page!</h4>
       <p>The Markup Validator can not do this for you. You may want to have a look
	at tools such as <a href="http://tidy.sourceforge.net">HTML Tidy</a>.</p>

    <h4 id="icon">My document is valid, can I use your "valid" icon?</h4>
  <h5>Practical use of the icon</h5>
  <p>
      <img class="inline-badge" src="http://www.w3.org/Icons/valid-xhtml10" alt="Valid XHTML 1.0!" height="31" width="88" />
      Yes. To show readers that one has taken some care to create an
      interoperable Web page, a "W3C valid" badge may be displayed 
      (here, the "valid XHTML 1.0" badge) <strong>on any page
      that validates</strong>. 
  </p>
  <p>
   We encourage you to use the XHTML code below (or its HTML equivalent),
   but you may use a different code to integrate the icon within your web page
   as long as the icon is used as a link to revalidate the Web page it is in.
   Sample code is as follows:
  </p>
  <pre>
   &lt;p&gt;
      &lt;a href="http://validator.w3.org/check/referer"&gt;&lt;img
          src="http://www.w3.org/Icons/valid-xhtml10"
          alt="Valid XHTML 1.0!" height="31" width="88" /&gt;&lt;/a&gt;
    &lt;/p&gt;
  </pre>
  <h5>License and Guidelines for usage of the "valid" icons</h5>
  <p>Web content providers are granted the right to use the "W3C valid" logo
  on pages that pass validation (through the use of the 
  <a href="http://validator.w3.org/">W3C Markup Validator</a>) 
  for the W3C technology represented by the icon, and <strong>only</strong> 
  on pages that pass validation. 
  The icon must be used as a link to revalidate the Web page, thus providing
  a way to verify the page author's assertion that it passed validation.</p>
  
  <p>Note that "W3C Valid" icons are not an endorsement by the W3C of the page's 
  author, the substantive content of the page, nor its design. 
  Instead, the icons are <strong>only</strong> a mechanism to identify 
  pages that have been determined to be valid, and to easily 
  revalidate pages as often as as they are modified.</p>

  <p>Consequently, the use of the badge is in accordance with and governed by 
  the W3C <a href="http://www.w3.org/Consortium/Legal/trademark-license">Trademark License</a> 
  and <a href="http://www.w3.org/Consortium/Legal/logo-usage-20000308.html">Logo and Icon usage</a>
  policy.</p>

</div>

<div>
<h3 id="very-faq">Miscellaneous (Very) Frequently Asked Questions</h3>
    <h4 id="faq-doctype">No DOCTYPE Declaration Found!</h4>
      <p>
        A DOCTYPE Declaration is mandatory for most current markup languages
        and without one it is impossible to reliably validate a document.
      </p>

    <p>
      One should place a DOCTYPE declaration as the very first thing in an
      HTML document. For example, for a typical <a
      href="http://www.w3.org/TR/xhtml1/">XHTML 1.0</a> document:
    </p>
    <pre>
      &lt;!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
        "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"&gt;
      &lt;html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"&gt;
        &lt;head&gt;

          &lt;title&gt;Title&lt;/title&gt;
        &lt;/head&gt;

        &lt;body&gt;
          &lt;!-- ... body of document ... --&gt;
        &lt;/body&gt;

      &lt;/html&gt;
    </pre>
    <p>
      For XML documents, you may also wish to include an "XML Declaration"
      even before the DOCTYPE Declaration, but this is not well supported
      in older browsers. More information about this can be found in the
      <a href="http://www.w3.org/TR/xhtml1/">XHTML 1.0</a> Recommendation.
    </p>
      <p>
        The W3C QA Activity maintains a <a
          href="http://www.w3.org/QA/2002/04/valid-dtd-list.html">List of
            Valid Doctypes</a> that you can choose from, and the <acronym
          title="Web Design Group">WDG</acronym> maintains a document on
        "<a href="http://htmlhelp.com/tools/validator/doctype.html">Choosing
           a DOCTYPE</a>".
      </p>
    <h4 id="faq-charset"><q>No Character Encoding Found! </q></h4>

      <p>An HTML document should be served along with its character encoding.</p>

      <p> Specifying a character encoding is normally done in the web server
      configuration file or administration program. The <a
        href="http://www.w3.org/"><abbr
          title="World Wide Web Consortium">W3C</abbr></a> <a
        href="http://www.w3.org/International/"><abbr
          title="Internationalization">I18N</abbr> Activity</a> has collected
        <a href="http://www.w3.org/International/O-HTTP-charset"
           title="A Few Tips On How To Specify The Character Encoding">a few
          tips on how to do this</a> in popular web server implementations.
</p>
    <p>
      <a href="http://www.iana.org/"><abbr
      title="Internet Assigned Numbers Authority">IANA</abbr></a>
      maintains the list of <a
      href="http://www.iana.org/assignments/character-sets">official
      names for character sets</a> and the <abbr
        title="Web Design Group">WDG</abbr> has some <a
        href="http://www.htmlhelp.com/tools/validator/charset.html">information
        to help you correctly specify the character encoding</a>.
    </p>
    <p>
      To quickly check whether the document would validate after addressing
      the missing character encoding information, you can use the "Encoding"
      form control (accesskey "2") earlier in the page to force an encoding
      override to take effect. "iso-8859-1" (Western Europe and North America)
      and "utf-8" (Universal, but not commonly used in legacy documents) are
      common encodings if you are not sure what encoding to choose.
    </p>



    <h4 id="faq-ampersand">The validator complains about "&amp;" in my URLs!</h4>
<p>Most probably, you should read the <a 
href="http://www.htmlhelp.com/tools/validator/problems.html#amp">ampersand section</a>
of WDG's excellent 
"<a href="http://www.htmlhelp.com/tools/validator/problems.html">common validation problem</a>"
</p>

    <h4 id="faq-javascript">The validator complains about something in my JavaScript!</h4>
      <p>Most probably, you should read the 
	<a href="http://www.htmlhelp.com/tools/validator/problems.html#script">script section</a>
	of WDG's excellent
        <a href="http://www.htmlhelp.com/tools/validator/problems.html">Common HTML Validation Problems</a>
         document.
      </p>

    <h4 id="faq-linkandmeta">Why doesn't the validator like my 
    &lt;link ... /&gt; or &lt;meta ... /&gt;?</h4>
       <p>HTML is based on <a href="sgml.html">SGML</a> and uses an SGML 
	feature (called SHORTTAG) (note that this is <strong>not</strong> 
	the case with XHTML).</p>

      <p>With this feature enabled, the "/" in &lt;link ... /&gt; or &lt;meta ... /&gt;
	already closes the link (or meta) tag, and the "&gt;" becomes some regular text,
	which is not allowed in the &lt;head&gt; element. Since &lt;/head&gt;&lt;body&gt; 
	is optional in HTML (again, <strong>not</strong> in XHTML), it is silently inserted, 
	thus head-only elements like meta and style as well as 
	"&lt;/head&gt;" and "&lt;body&gt;", which may appear only once, become false.
      </p>

      <p>(explanation courtesy of Christoph P&auml;per)</p>

    <h4 id="faq-typo">I found some nasty typo like &lt;p&lt;a ...&gt; 
    and the validator accepted it!</h4>

      <p>This again (as in the <a href="#faq-linkandmeta">previous case</a>) comes from the
	SHORTTAG feature in HTML (<strong>not</strong> in XHTML). The typo is actually a 
	"shorthand markup" and is a valid construct in HTML, even though its use 
	<a href="http://www.w3.org/TR/html4/appendix/notes.html#h-B.3.7">is not recommended</a>.
      </p>

    <h4 id="faq-referer">/check/referer does not work - or - the validator says it does not support 
    my "undefined" URL scheme</h4>

      <p>Browsers and other Web agents usually send information about the page they come from, in a 
      <code>Referer</code> header. The validator uses this information for a features that allows 
      it to validate whatever page the browser last visited. The "valid" icons on some Web page usually
      point to the validation of the page using this feature.</p>

      <p>Unfortunately, some zealous "security software" or Web proxies strip the referrer 
      information from what the browser sends. Without this information the validator is not able to
      find what the URL of the document to validate is, and gives the same error message as when it is
      given a type of URL it does not understand.</p>

      <p><strong>How to fix</strong>:</p>
      <ul>
	<li>Check that it is indeed the <code>Referer</code> issue. The validator should have redirected you to
	<code>http://validator.w3.org/check?uri=</code>. Otherwise, check the address you have given the validator.</li>
	<li>The validator can not fix this issue. You will have to (ask your administrator to) reconfigure
	whichever zealous software is stripping this referrer info.</li>
	<li>If you have a link on your page using the "/check/referer" feature, you could replace them with the
	a link to the validator without this feature, e.g. <code>http://validator.w3.org/check?uri=http://www.example.com</code></li>
	<li>If you have no control over the page or annoying software, simply append the address of the page you wanted validated
	to the <code>http://validator.w3.org/check?uri=</code> address.</li>
     </ul>
</div>
</div>
<!--#include virtual="../footer.html" -->
  </body>
</html>