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<!--#set var="revision" value="\$Id: help.html,v 1.13 2003-02-24 23:33:19 ville Exp $"
--><!--#set var="date" value="\$Date: 2003-02-24 23:33:19 $"
--><!--#set var="title" value="Help for The W3C Markup Validation Service"
--><!--#set var="relroot" value="../"
--><!--#include virtual="../header.html" -->
<div id="toc">
<h2 id="TableOfContents">Table of contents</h2>
<ul>
<li>About the Markup Validator
<ul>
<li>
<a href="#what-is-it">What is the Markup Validator and what does it do?</a>
</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>
</ul>
</li>
<li>Using this service
<ul>
<li>
<a href="#manual">How do I use the Markup validator?</a>
</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>
</ul>
</li>
<li>Miscellaneous (Very) Frequently Asked Questions
<ul>
<li>
<a href="#faq-ampersand">The validator complains about "&" 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 <link ... />
or <meta ... />?</a>
</li>
<li>
<a href="#faq-typo">I found some nasty typo like <p<a ...>
and the validator accepted it!</a>
</li>
</ul>
</li>
</ul>
</div>
<div id="skip">
<h2 id="about">About the Markup Validator</h2>
<h3 id="what-is-it">What is the Markup Validator and what does it do?</h3>
<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>
<h3 id="why-validate">Why should I validate my HTML pages?</h3>
<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>
<h3 id="who-does-validator">Who owns/maintain the Markup Validator?</h3>
<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="http://validator.w3.org:8001/about.html#credits">full credits</a>)
</p>
<h3 id="others">What other validators are there?</h3>
<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>
<h3 id="how">How does The Validator work?</h3>
<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>
<h3 id="howto-feedback">How do I send feedback/bug reports about the Markup Validator?</h3>
<p>Read the instructions on our <a href="../feedback.html">Feedback page</a>.</p>
</div>
<div>
<h2 id="using">Using this service</h2>
<h3 id="manual">How do I use this service?</h3>
<p>
Most probably, you will want to use the online Markup Validation service.
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>
<h3 id="errors">What are these error messages?</h3>
<p>The output of the Markup Validator may be hard to decypher for
newcomers and experts alike, so we are maintaining a <a
href="http://validator.w3.org:8001/docs/errors.html">list of error
messages and their interpretation</a>, which should help.
</p>
<h3 id="munged-doctype">Many error messages? Don't panic.</h3>
<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
— 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>
<h3 id="cleanup">I don't want error messages, I want you to clean up my page!</h3>
<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>
</div>
<div>
<h2 id="very-faq">Miscellaneous (Very) Frequently Asked Questions</h2>
<h3 id="faq-ampersand">The validator complains about "&" in my URLs!</h3>
<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>
<h3 id="faq-javascript">The validator complains about something in my Javascript!</h3>
<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 validation problem</a>"
</p>
<h3 id="faq-linkandmeta">Why doesn't the validator like my
<link ... /> or <meta ... />?</h3>
<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 <link ... /> or <meta ... />
already closes the link (or meta) tag, and the ">" becomes some regular text,
which is not allowed in the <head> element. Since </head><body>
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
"</head>" and "<body>", which may apear only once, become false.
</p>
<p>(explanation courtesy of Christoph Päper)</p>
<h3 id="faq-typo">I found some nasty typo like <p<a ...>
and the validator accepted it!</h3>
<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>
</div>
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