mirror of
https://github.com/ezyang/htmlpurifier.git
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232 lines
8.6 KiB
HTML
232 lines
8.6 KiB
HTML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
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"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"><head>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<meta name="description" content="Tutorial for tweaking HTML Purifier's Tidy-like behavior." />
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<link rel="stylesheet" type="text/css" href="style.css" />
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<title>Tidy - HTML Purifier</title>
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</head><body>
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<h1>Tidy</h1>
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<div id="filing">Filed under Development</div>
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<div id="index">Return to the <a href="index.html">index</a>.</div>
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<div id="home"><a href="http://htmlpurifier.org/">HTML Purifier</a> End-User Documentation</div>
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<p>You've probably heard of HTML Tidy, Dave Raggett's little piece
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of software that cleans up poorly written HTML. Let me say it straight
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out:</p>
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<p class="emphasis">This ain't HTML Tidy!</p>
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<p>Rather, Tidy stands for a cool set of Tidy-inspired features in HTML Purifier
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that allows users to submit deprecated elements and attributes and get
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valid strict markup back. For example:</p>
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<pre><center>Centered</center></pre>
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<p>...becomes:</p>
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<pre><div style="text-align:center;">Centered</div></pre>
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<p>...when this particular fix is run on the HTML. This tutorial will give
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you the lowdown of what exactly HTML Purifier will do when Tidy
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is on, and how to fine-tune this behavior. Once again, <strong>you do
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not need Tidy installed on your PHP to use these features!</strong></p>
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<h2>What does it do?</h2>
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<p>Tidy will do several things to your HTML:</p>
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<ul>
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<li>Convert deprecated elements and attributes to standards-compliant
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alternatives</li>
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<li>Enforce XHTML compatibility guidelines and other best practices</li>
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<li>Preserve data that would normally be removed as per W3C</li>
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</ul>
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<h2>What are levels?</h2>
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<p>Levels describe how aggressive the Tidy module should be when
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cleaning up HTML. There are four levels to pick: none, light, medium
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and heavy. Each of these levels has a well-defined set of behavior
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associated with it, although it may change depending on your doctype.</p>
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<dl>
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<dt>light</dt>
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<dd>This is the <strong>lenient</strong> level. If a tag or attribute
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is about to be removed because it isn't supported by the
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doctype, Tidy will step in and change into an alternative that
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is supported.</dd>
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<dt>medium</dt>
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<dd>This is the <strong>correctional</strong> level. At this level,
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all the functions of light are performed, as well as some extra,
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non-essential best practices enforcement. Changes made on this
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level are very benign and are unlikely to cause problems.</dd>
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<dt>heavy</dt>
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<dd>This is the <strong>aggressive</strong> level. If a tag or
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attribute is deprecated, it will be converted into a non-deprecated
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version, no ifs ands or buts.</dd>
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</dl>
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<p>By default, Tidy operates on the <strong>medium</strong> level. You can
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change the level of cleaning by setting the %HTML.TidyLevel configuration
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directive:</p>
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<pre>$config->set('HTML.TidyLevel', 'heavy'); // burn baby burn!</pre>
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<h2>Is the light level really light?</h2>
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<p>It depends on what doctype you're using. If your documents are HTML
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4.01 <em>Transitional</em>, HTML Purifier will be lazy
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and won't clean up your <code>center</code>
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or <code>font</code> tags. But if you're using HTML 4.01 <em>Strict</em>,
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HTML Purifier has no choice: it has to convert them, or they will
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be nuked out of existence. So while light on Transitional will result
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in little to no changes, light on Strict will still result in quite
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a lot of fixes.</p>
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<p>This is different behavior from 1.6 or before, where deprecated
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tags in transitional documents would
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always be cleaned up regardless. This is also better behavior.</p>
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<h2>My pages look different!</h2>
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<p>HTML Purifier is tasked with converting deprecated tags and
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attributes to standards-compliant alternatives, which usually
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need copious amounts of CSS. It's also not foolproof: sometimes
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things do get lost in the translation. This is why when HTML Purifier
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can get away with not doing cleaning, it won't; this is why
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the default value is <strong>medium</strong> and not heavy.</p>
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<p>Fortunately, only a few attributes have problems with the switch
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over. They are described below:</p>
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<table class="table">
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<thead><tr>
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<th>Element@Attr</th>
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<th>Changes</th>
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</tr></thead>
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<tbody>
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<tr>
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<td>caption@align</td>
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<td>Firefox supports stuffing the caption on the
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left and right side of the table, a feature that
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Internet Explorer, understandably, does not have.
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When align equals right or left, the text will simply
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be aligned on the left or right side.</td>
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</tr>
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<tr>
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<td>img@align</td>
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<td>The implementation for align bottom is good, but not
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perfect. There are a few pixel differences.</td>
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</tr>
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<tr>
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<td>br@clear</td>
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<td>Clear both gets a little wonky in Internet Explorer. Haven't
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really been able to figure out why.</td>
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</tr>
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<tr>
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<td>hr@noshade</td>
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<td>All browsers implement this slightly differently: we've
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chosen to make noshade horizontal rules gray.</td>
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</tr>
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</tbody>
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</table>
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<p>There are a few more minor, although irritating, bugs.
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Some older browsers support deprecated attributes,
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but not CSS. Transformed elements and attributes will look unstyled
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to said browsers. Also, CSS precedence is slightly different for
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inline styles versus presentational markup. In increasing precedence:</p>
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<ol>
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<li>Presentational attributes</li>
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<li>External style sheets</li>
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<li>Inline styling</li>
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</ol>
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<p>This means that styling that may have been masked by external CSS
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declarations will start showing up (a good thing, perhaps). Finally,
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if you've turned off the style attribute, almost all of
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these transformations will not work. Sorry mates.</p>
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<p>You can review the rendering before and after of these transformations
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by consulting the <a
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href="http://htmlpurifier.org/live/smoketests/attrTransform.php">attrTransform.php
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smoketest</a>.</p>
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<h2>I like the general idea, but the specifics bug me!</h2>
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<p>So you want HTML Purifier to clean up your HTML, but you're not
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so happy about the br@clear implementation. That's perfectly fine!
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HTML Purifier will make accomodations:</p>
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<pre>$config->set('HTML.Doctype', 'XHTML 1.0 Transitional');
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$config->set('HTML.TidyLevel', 'heavy'); // all changes, minus...
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<strong>$config->set('HTML.TidyRemove', 'br@clear');</strong></pre>
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<p>That third line does the magic, removing the br@clear fix
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from the module, ensuring that <code><br clear="both" /></code>
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will pass through unharmed. The reverse is possible too:</p>
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<pre>$config->set('HTML.Doctype', 'XHTML 1.0 Transitional');
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$config->set('HTML.TidyLevel', 'none'); // no changes, plus...
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<strong>$config->set('HTML.TidyAdd', 'p@align');</strong></pre>
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<p>In this case, all transformations are shut off, except for the p@align
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one, which you found handy.</p>
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<p>To find out what the names of fixes you want to turn on or off are,
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you'll have to consult the source code, specifically the files in
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<code>HTMLPurifier/HTMLModule/Tidy/</code>. There is, however, a
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general syntax:</p>
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<table class="table">
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<thead>
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<tr>
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<th>Name</th>
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<th>Example</th>
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<th>Interpretation</th>
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</tr>
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</thead>
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<tbody>
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<tr>
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<td>element</td>
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<td>font</td>
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<td>Tag transform for <em>element</em></td>
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</tr>
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<tr>
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<td>element@attr</td>
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<td>br@clear</td>
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<td>Attribute transform for <em>attr</em> on <em>element</em></td>
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</tr>
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<tr>
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<td>@attr</td>
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<td>@lang</td>
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<td>Global attribute transform for <em>attr</em></td>
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</tr>
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<tr>
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<td>e#content_model_type</td>
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<td>blockquote#content_model_type</td>
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<td>Change of child processing implementation for <em>e</em></td>
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</tr>
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</tbody>
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</table>
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<h2>So... what's the lowdown?</h2>
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<p>The lowdown is, quite frankly, HTML Purifier's default settings are
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probably good enough. The next step is to bump the level up to heavy,
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and if that still doesn't satisfy your appetite, do some fine-tuning.
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Other than that, don't worry about it: this all works silently and
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effectively in the background.</p>
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</body></html>
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<!-- vim: et sw=4 sts=4
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-->
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