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git-svn-id: http://htmlpurifier.org/svnroot/htmlpurifier/trunk@1066 48356398-32a2-884e-a903-53898d9a118a
242 lines
9.3 KiB
HTML
242 lines
9.3 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="Functional specification for HTML Purifier's advanced API for defining custom filtering behavior." />
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<link rel="stylesheet" type="text/css" href="style.css" />
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<title>Advanced API - HTML Purifier</title>
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</head><body>
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<h1>Advanced API</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>HTML Purifier currently natively supports only a subset of HTML's
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allowed elements, attributes, and behavior; specifically, this subset
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is the set of elements that are safe for untrusted users to use.
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However, HTML Purifier is often utilized to ensure standards-compliance
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from input that is trusted (making it a sort of Tidy substitute),
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and often users need to define new elements or attributes. The
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advanced API is oriented specifically for these use-cases.</p>
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<p>Our goals are to let the user:</p>
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<dl>
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<dt>Select</dt>
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<dd><ul>
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<li>Doctype</li>
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<li><em>Filterset</em></li>
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<li>Elements / Attributes / Modules</li>
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<li>Tidy</li>
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</ul></dd>
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<dt>Customize</dt>
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<dd><ul>
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<li>Attributes</li>
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<li>Elements</li>
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<li>Doctypes</li>
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</ul></dd>
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</dl>
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<h2>Select</h2>
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<p>For basic use, the user will have to specify some basic parameters. This
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is not strictly necessary, as HTML Purifier's default setting will always
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output safe code, but is required for standards-compliant output.</p>
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<h3>Selecting a Doctype</h3>
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<p>The first thing to select is the <strong>doctype</strong>. This
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is essential for standards-compliant output.</p>
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<p class="technical">This identifier is based
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on the name the W3C has given to the document type and <em>not</em>
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the DTD identifier, although that may be included as an alias.</p>
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<p>This parameter is set via the configuration object:</p>
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<pre>$config->set('HTML', 'Doctype', 'XHTML 1.0 Transitional');</pre>
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<p>Due to historical reasons, the default doctype is XHTML 1.0
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Transitional, however, we really shouldn't be guessing what the user's
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doctype is. Fortunantely, people who can't be bothered to set this won't
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be bothered when their pages stop validating.</p>
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<h3>Selecting Elements / Attributes / Modules</h3>
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<p>HTML Purifier will, by default, allow as many elements and attributes
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as possible. However, a user may decide to roll their own filterset by
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selecting modules, elements and attributes to allow for their own
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specific use-case.</p>
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<p class="technical">The currently un-documented Filterset interface
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will offer a way of encapsulating the following declarations, so that
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a user can pick a recipe of tags that is thought to be commonly used.</p>
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<p>In practice, this is the most commonly demanded feature. Most users are
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perfectly happy defining a filterset that looks like:</p>
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<pre>$config->setAllowedHTML('a[href,title];em;p;blockquote');</pre>
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<p class="technical">The directive %HTML.Allowed is a convenience function
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that may be fully expressed with the legacy interface, and thus is
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given its own setter, or implemented by intercepting the set() function
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call, parsing, and assigning to the finer grained directives accordingly.</p>
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<p>We currently support a separated interface, which also must be preserved:</p>
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<pre>$config->set('HTML', 'AllowedElements', 'a,em,p,blockquote');
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$config->set('HTML', 'AllowedAttributes', 'a.href,a.title');</pre>
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<p>A user may also choose to allow modules:</p>
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<pre>$config->set('HTML', 'AllowedModules', 'Hypertext,Text,Lists'); // or
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$config->setAllowedHTML('Hypertext,Text,Lists');</pre>
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<p>But it is not expected that this feature will be widely used.</p>
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<p class="technical">Module selection will work slightly differently
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from the other AllowedElements and AllowedAttributes directives by
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directly modifying the doctype you are operating in. You cannot,
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however, add modules: there is a separate interface for that.</p>
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<p class="technical">Modules are distinguished from regular elements by the
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case of their first letter. While XML distinguishes between and allows
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lower and uppercase letters in element names, XHTML uses only lower-case
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element names for sake of consistency.</p>
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<h3>Selecting Tidy</h3>
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<p>The name of this segment of functionality is inspired off of Dave
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Ragget's program HTML Tidy, which purported to help clean up HTML. In
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HTML Purifier, Tidy functionality involves turning unsupported and
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deprecated elements into standards-compliant ones, maintaining
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backwards compatibility, and enforcing best practices.</p>
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<p>Tidy is optional, when on, it has several coarse
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levels of operations, as well as directives that can be used to fine-tune
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the output. The coarse levels, set at %HTML.TidyLevel, are:</p>
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<dl>
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<dt>Lenient</dt>
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<dd>Preserve any non standards-compliant aspects by transforming
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them into standards-compliant equivalents.</dd>
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<dt>Correctional</dt>
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<dd>Default: Be lenient and enforce good practices.</dd>
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<dt>Aggressive</dt>
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<dd>Be correctional and transform as many deprecated elements as
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possible to CSS forms</dd>
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</dl>
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<p>The distinction between correctional and aggressive is fuzzy,
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so the user will also have %HTML.TidyAdd and %HTML.TidyRemove, in
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which they may list the names of transforms they want and don't want,
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using the broad level as a starting point. The naming convention
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has not been established yet, but it will be something along the lines
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of 'element.attribute', with globs and special cases supported.</p>
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<h3>Unified selector</h3>
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<p>Because selecting each and every one of these configuration options
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is a chore, we may wish to offer a specialized configuration method
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for selecting a filterset. Possibility:</p>
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<pre>function selectFilter($doctype, $filterset, $tidy)</pre>
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<p>...which is simply a light wrapper over the individual configuration
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calls. A custom config file format or text format could also be adopted.</p>
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<h2>Customize</h2>
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<p>By reviewing topic posts in the support forum, we determined that
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there were two primarily demanded customization features people wanted:
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to add an attribute to an existing element, and to add an element.
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Thus, we'll want to create convenience functions for these common
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use-cases.</p>
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<p>Note that the functions described here are only available if
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a raw copy of <code>HTMLPurifier_HTMLDefinition</code> was retrieved.
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<code>addAttribute</code> may work on a processed copy, but for
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consistency's sake we will mandate this for everything.</p>
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<h3>Attributes</h3>
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<p>An attribute is bound to an element by a name and has a specific
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<code>AttrDef</code> that validates it. Thus, the interface should
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be:</p>
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<pre>function addAttribute($element, $attribute, $attribute_def);</pre>
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<p>With a use-case that looks like:</p>
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<pre>$def->addAttribute('a', 'rel', new HTMLPurifier_AttrDef_Enum(array('nofollow')));</pre>
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<p>The <code>$attribute_def</code> value can be a little flexible,
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to make things simpler. We'll let it also be:</p>
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<ul>
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<li>Class name: We'll instantiate it for you</li>
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<li>Function name: We'll create an <code>HTMLPurifier_AttrDef_Anonymous</code>
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class with that function registered as a callback.</li>
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<li>String attribute type: We'll use <code>HTMLPurifier_AttrTypes</code>
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</li>
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<li>String starting with <code>enum(</code>: We'll explode it and stuff it in an
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<code>HTMLPurifier_AttrDef_Enum</code> for you.</li>
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</ul>
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<p>Making the previous example written as:</p>
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<pre>$def->addAttribute('a', 'rel', 'enum(nofollow)');</pre>
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<h3>Elements</h3>
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<p>An element requires certain information as specified by
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<code>HTMLPurifier_ElementDef</code>. However, not all of it is necessary,
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the usual things required are:</p>
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<ul>
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<li>Attributes</li>
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<li>Content model/type</li>
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<li>Registration in a content set</li>
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</ul>
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<p>This suggests an API like this:</p>
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<pre>function addElement($element, $type, $contents,
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$attr_collections = array(); $attributes = array());</pre>
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<p>Each parameter explained in depth:</p>
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<dl>
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<dt><code>$element</code></dt>
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<dd>Element name, ex. 'label'</dd>
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<dt><code>$type</code></dt>
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<dd>Content set to register in, ex. 'Inline' or 'Flow'</dd>
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<dt><code>$contents</code></dt>
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<dd>Description of allowed children. This is a merged form of
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<code>HTMLPurifier_ElementDef</code>'s member variables
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<code>$content_model</code> and <code>$content_model_type</code>,
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where the form is <q>Type: Model</q>, ex. 'Optional: Inline'.
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There are also a number of predefined templates one may use.</dd>
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<dt><code>$attr_collections</code></dt>
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<dd>Array (or string if only one) of attribute collection(s) to
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merge into the attributes array.</dd>
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<dt><code>$attributes</code></dt>
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<dd>Array of attribute names to attribute definitions, much like
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the above-described attribute customization.</dd>
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</dl>
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<p>A possible usage:</p>
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<pre>$def->addElement('font', 'Inline', 'Optional: Inline', 'Common',
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array('color' => 'Color'));</pre>
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<p>See <code>HTMLPurifier/HTMLModule.php</code> for details.</p>
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<div id="version">$Id$</div>
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</body></html> |