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git-svn-id: http://htmlpurifier.org/svnroot/htmlpurifier/trunk@928 48356398-32a2-884e-a903-53898d9a118a
287 lines
11 KiB
HTML
287 lines
11 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://hp.jpsband.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. This is by design,
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but as the user is always right, they'll need some method to overload
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these behaviors.</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>Mode: Lenient / Correctional</li>
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<li>Elements / Attributes / Modules</li>
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<li>Filterset</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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</ul></dd>
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<dt>Internals</dt>
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<dd><ul>
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<li>Modules / Elements / Attributes / Attribute Types</li>
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<li>Filtersets</li>
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<li>Doctype</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.</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 Mode</h3>
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<p>Within doctypes, there are various <strong>modes</strong> of operation.
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These indicate variant behaviors that, while not strictly changing the
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allowed set of elements and attributes, definitely affect the output.
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Currently, we have two modes, which may be used together:</p>
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<dl>
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<dt>Lenient</dt>
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<dd>
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<p>Deprecated elements and attributes will be transformed into
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standards-compliant alternatives when explicitly disallowed.</p>
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<p>For example, in the XHTML 1.0 Strict doctype, a <code>center</code>
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element would be turned into a <code>div</code> with the CSS property
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<code>text-align:center;</code>, but in XHTML 1.0 Transitional
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the element would be preserved.</p>
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<p>This mode is on by default.</p>
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</dd>
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<dt>Correctional[items to correct]</dt>
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<dd>
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<p>Deprecated elements and attributes will be transformed into
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standards-compliant alternatives whenever possible.
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It may have various levels of operation.</p>
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<p>Referring back to the previous example, the <code>center</code> element would
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be transformed in both cases. However, elements without a
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reasonable standards-compliant alternative will be preserved
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in their form.</p>
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<p>A user may want to correct certain deprecated attributes, but
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not others. For example, the <code>bgcolor</code> attribute may be
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acceptable, but the <code>center</code> element not; also, possibly,
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an HTML Purifier transformation may be buggy, so the user wants
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to forgo it. Thus, correctional accepts an array defining which
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elements and attributes to cleanup, or no parameter at all, which
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means everything gets corrected. This also means that each
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correction needs to be given a unique ID that can be referenced
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in this manner. (We may also allow globbing, like *.name or a.*
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for mass-enabling correction, and subtractive mode, where things
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specified stop correction.) This array gets passed into the
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constructor of the mode's module.</p>
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<p>This mode is on by default.</p>
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</dd>
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</dl>
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<p>A possible call to select modes would be:</p>
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<pre>$config->set('HTML', 'Mode', array('correctional', 'lenient'));</pre>
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<p>If modes have extra parameters, a hash is necessary:</p>
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<pre>$config->set('HTML', 'Mode', array(
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'correctional' => 'center,a.name',
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'lenient' => true // this one's just boolean
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));</pre>
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<p>Modes may be specified along with the doctype declaration (we may want
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to get a better set of separator characters):</p>
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<pre>$config->setDoctype('XHTML Transitional 1.0', '+correctional[center,a.name] -lenient');</pre>
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<p>
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With regards to the various levels of operation conjectured in the
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Correctional mode, this is prompted by the fact that a user may want to
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correct certain problems but not others, for example, fix the <code>center</code>
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element but not the <code>u</code> element, both of which are deprecated.
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Having an integer <q>level</q> will not work very well for such fine
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grained tweaking, but an array of specific settings might.</p>
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<h3>Selecting Elements / Attributes / Modules</h3>
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<p></p>
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<p>If this cookie cutter approach doesn't appeal to a user, they may
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decide to roll their own filterset by selecting modules, elements and
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attributes to allow.</p>
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<p class="technical">This would make use of the same facilities
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as a filterset author would use, except that it would go under an
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<q>anonymous</q> filterset that would be auto-selected if any of the
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relevant module/elements/attribute selection configuration directives were
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non-null.</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>$config->setAllowedHTML('a[href,title];em;p;blockquote');</pre>
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<p class="technical">The directive %HTML.Allowed is a convenience function
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that may be fully expressed with the legacy interface, and thus is
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given its own setter.</p>
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<p>We currently support a separated interface, which also must be preserved:</p>
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<pre>$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="fixme">The granularity of these modules is too coarse for
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the average user (for example, the core module loads everything from
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the essential <code>p</code> element to the not-so-safe <code>h1</code>
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element). How do we make this still a viable solution? Possible answers
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may be sub-modules or module parameters. This may not even be a problem,
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considering that most people won't be selecting modules.</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, most well-known XML
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languages use only lower-case
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element names for sake of consistency.</p>
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<p class="technical">Considering that, internally speaking, as mandated by
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the XHTML 1.1 Modularization specification, we have organized our
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elements around modules, considerable gymnastics will be needed to
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get this sort of functionality working.</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, $mode)</pre>
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<p>...which is simply a light wrapper over the individual configuration
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calls. A custom config file format or text format could also be adopted.</p>
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<h2>Customize</h2>
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<p>By reviewing topic posts in the support forum, we determined that
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there were two primarily demanded customization features people wanted:
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to add an attribute to an existing element, and to add an element.
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Thus, we'll want to create convenience functions for these common
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use-cases.</p>
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<p>Note that the functions described here are only available if
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a raw copy of <code>HTMLPurifier_HTMLDefinition</code> was retrieved.
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<code>addAttribute</code> may work on a processed copy, but for
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consistency's sake we will mandate this for everything.</p>
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<h3>Attributes</h3>
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<p>An attribute is bound to an element by a name and has a specific
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<code>AttrDef</code> that validates it. Thus, the interface should
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be:</p>
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<pre>function addAttribute($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, $content_model, $attributes = array());</pre>
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<p>Each parameter explained in depth:</p>
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<dl>
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<dt><code>$element</code></dt>
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<dd>Element name, ex. 'label'</dd>
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<dt><code>$type</code></dt>
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<dd>Content set to register in, ex. 'Inline' or 'Flow'</dd>
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<dt><code>$content_model</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'.</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',
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array(0 => array('Common'), 'color' => 'Color'));</pre>
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<p>We may want to Common attribute collection inclusion to be added
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by default.</p>
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<div id="version">$Id$</div>
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</body></html> |