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     <h1 id="title"><a href="http://www.w3.org/"><img alt="W3C" width="110" height="61" id="logo" src="./images/w3c.png" /></a>
     <a href="./"><span>CSS Validation Service</span></a></h1>
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       Check Cascading Style Sheets (CSS) and (X)HTML documents with style sheets
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      <h2>About the CSS Validator</h2>

<h3 id="TableOfContents">Table of contents</h3>
<div id="toc">
<ol>
  <li>About this Service
  <ol>
<li><a href="#what">What is this? Do I need it?</a></li>
<li><a href="#help">The explanation above is incomprehensible! Help!</a></li>
<li><a href="#reference">So, this is the authority on what is correct CSS and what isn't?</a></li>
<li><a href="#validCSS">What does “Valid CSS” mean? Which version of CSS does this validator use?</a></li>
<li><a href="#free">How much does it cost?</a></li>
<li><a href="#who">Who wrote this tool? Who maintains it?</a></li>
<li><a href="#contact">How do I contact the authors? Report a bug?</a></li>
<li><a href="#participate">Can I help?</a></li>
  </ol>
  </li>
  <li>Developers' corner
  <ol>
    <li><a href="#code">What is the CSS Validator written in? Is the source available somewhere?</a></li>
    <li><a href="#install">Can I install and run the CSS Validator myself?</a></li>
    <li><a href="#api">Can I build an application upon this validator? Is there an API?</a></li>
  </ol>
  </li>
</ol>
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<h3 id="about">About this Service</h3>

<h4 id="what">What is this? Do I need it?</h4>

<p>The W3C CSS Validation Service is a free software created by the W3C 
to help Web designers and Web developers check Cascading Style Sheets (CSS). 
It can be used on this <a href="./">free service</a> on the web, or downloaded 
and used either as a java program, or as a java servlet on a Web server.</p>

<p>Do <em>you</em> need it? If you are a Web developer or a Web designer, this 
tool will be an invaluable ally. Not only will it compare your style sheets to the 
CSS specifications, helping you find errors, typos, or incorrect uses of CSS, it will
also tell you when your CSS poses some risks in terms of usability.</p>

<h4 id="help">The explanation above is incomprehensible! Help!</h4>
<p>Most documents on the Web are written in a computer language called HTML. This language
can be used to create pages with structured information, links, and multimedia objects. For 
color, text, and layout, HTML uses a styling language called CSS, short for "Cascading Style Sheets". 
What this tool does is help people authoring CSS check, and fix if necessary, their CSS Style Sheets.</p>

<h4 id="reference">So, this is the authority on what is correct CSS and what isn't?</h4>
<p>No. It is a helpful and reliable tool, but a software tool, and like every software, it has some
<a href="http://www.w3.org/Bugs/Public/buglist.cgi?product=CSSValidator">bugs and issues</a>.
The actual reference on Cascading Style Sheets are the <a href="http://www.w3.org/Style/CSS/#specs">CSS 
Specifications</a>.</p>

<h4 id="validCSS">What does “Valid CSS” mean? Which version of CSS does this validator use?</h4>
<p>According to the <a href="http://www.w3.org/TR/CSS21/conform.html#valid-style-sheet" 
title="CSS 2.1 Specification – Conformance: requirements and recommendations">CSS 2.1 Specification</a>:
<q cite="http://www.w3.org/TR/CSS21/conform.html">The validity of a style sheet depends on the level of 
CSS used for the style sheet. […]  valid CSS 2.1 style sheet must be written according to the grammar of CSS 2.1. 
Furthermore, it must contain only at-rules, property names, and property values defined in this specification.</q></p>

<p>By default, this validator checks style sheets against the grammar, properties and values defined in the 
<a href="http://www.w3.org/TR/CSS21/" 
title="Cascading Style Sheets Level 2 Revision 1 (CSS&nbsp;2.1) Specification">CSS&nbsp;2.1</a> specification, 
but other CSS profiles can be checked against by using the options.</p>

<p>CSS is an evolving language, and it is considered by many that “CSS” is a single grammar 
(the one defined in the latest specification) with a number of properties and acceptable 
values defined in various profiles.In a future version of this validator, the default behavior may be to check
style sheets against that latest “CSS grammar” and the cloud of all standardized CSS properties and values.</p>

<h4 id="free">How much does it cost?</h4>
<p>Nothing. The service is free. The source is <a href="DOWNLOAD.html">open</a> and you are free
to download it, use it, modify it, distribute it, 
and <a href="http://www.w3.org/Consortium/Legal/copyright-software">more</a>.
If you really like it, you are welcome to <a href="#participate">join the project</a> or donate to W3C via the
 <a href="http://www.w3.org/Consortium/sup">W3C supporters program</a>, but nobody forces you to.</p>

<h4 id="who">Who wrote this tool? Who maintains it?</h4>
<p>W3C maintains and hosts the tool, thanks to the work and contributions by W3C staff,
volunteer developers and translators. See the <a href="thanks.html">credits and acknowledgments page</a>
for details. <a href="#participate">You too can help</a>.</p>

<h4 id="participate">Can I help?</h4>
<p>Of course. If you are a java programmer, you can help the CSS Validator project by 
checking out the <a href="#code">code</a>,
adopting and fixing <a href="http://www.w3.org/Bugs/Public/buglist.cgi?product=CSSValidator">bugs</a>,
or helping build new features.</p>
<p>But you do not need to be a coder to help build and maintain this tool: you can also help improve the 
documentation, participate in translating the validator in your language, or subscribe to the 
<a href="http://lists.w3.org/Archives/Public/www-validator-css/">mailing-list</a> and discuss about the tool
or help other users.</p>

<h4 id="contact">Any other question?</h4>
<p>If you have any question regarding CSS or the CSS validator, check out the available
<a href="Email">mailing-lists and forums</a>. But before that, make sure that your question
or comment is not covered already by the <a href="http://www.websitedev.de/css/validator-faq">CSS Validator 
<acronym title="Frequently Asked Questions">FAQ</acronym> document</a>.</p>


<h3 id="dev">Developers' corner</h3>
<h4 id="code">What is the CSS Validator written in? Is the source available somewhere?</h4>
<p>The W3C CSS validator is written using the java language, and yes, its source 
is available, using CVS: you can 
<a href="http://dev.w3.org/cvsweb/2002/css-validator/">browse the code online</a> 
or follow the instructions there to download the whole source tree. For a quick
overview of the classes used in the CSS Validator code, check out the 
<a href="README.html">README</a> file.</p>

<h4 id="install">Can I install and run the CSS Validator myself?</h4>
<p>It is possible to download and install the CSS validator, and to run it either from the command line, or 
as a servlet in a Web server. Read the <a href="RUN.html">instructions</a> for installation and use.</p>

<h4 id="api">Can I build an application upon this validator? Is there an API?</h4>
<p>Yes, and <a href="api.html">yes</a>. The CSS Validator has a (RESTful) <a href="api.html">SOAP interface</a>
which should make it reasonably easy to build applications (Web or otherwise) upon it. Good manners and 
respectful usage of shared resources are of course customary: make sure your applications sleep() between
calls to the validator, or install and run your own instance of the validator.</p>
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