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Update Advanced API with various edits and Customization section.
git-svn-id: http://htmlpurifier.org/svnroot/htmlpurifier/trunk@928 48356398-32a2-884e-a903-53898d9a118a
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Edward Z. Yang
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@ -16,9 +16,10 @@
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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>It makes no sense to adopt a <q>one-size-fits-all</q> approach to
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filtersets: therefore, users must be able to define their own sets of
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<q>allowed</q> elements, as well as switch in-between doctypes of HTML.</p>
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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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@ -26,20 +27,18 @@ filtersets: therefore, users must be able to define their own sets of
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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>Filtersets: Rich / Plain / Full ...</li>
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<li>Mode: Lenient / Correctional</li>
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<li>Collections (?): Safe / Unsafe</li>
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<li>Tags / Attributes / Modules</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>Tags / Attributes / Attribute Types</li>
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<li>Filtersets</li>
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<li>Root Node</li>
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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>Create</dt>
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<dt>Internals</dt>
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<dd><ul>
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<li>Modules / Tags / Attributes / Attribute Types</li>
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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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@ -47,11 +46,14 @@ filtersets: therefore, users must be able to define their own sets of
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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>By default, users will use a doctype-based, permissive but secure
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whitelist. They must define a <strong>doctype</strong>, and this serves
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as the first method of determining a filterset.</p>
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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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@ -61,114 +63,106 @@ the DTD identifier.</p>
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<pre>$config->set('HTML', 'Doctype', 'XHTML 1.0 Transitional');</pre>
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<p>Due to legacy, the default option is XHTML 1.0 Transitional, however, we
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really shouldn't be guessing what the user's doctype is. Fortunantely,
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people who can't be bothered to set this won't be bothered when their
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pages stop validating.</p>
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<h3>Selecting a Filterset</h3>
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<p>However, selecting this doctype doesn't mean much, because if we
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adhered exactly to the definition we would be letting XSS and other
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nasties through. HTML Purifier must, in its filterset, allow a subset
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of the doctype, which we shall call a <strong>filterset</strong>.</p>
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<p>By default, HTML Purifier will use the <strong>Rich</strong>
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filterset, which allows as many elements as possible with untrusted
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sources. Other possible filtersets could be:</p>
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<dl>
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<dt>Full</dt>
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<dd>Allows the full span of elements in the doctype, good if you want
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HTML Purifier to work as a Tidy substitute but not to strip
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anything out.</dd>
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<dt>Plain</dt>
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<dd>Provides a minimum set of tags for semantic markup of things
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like blog comments.</dd>
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</dl>
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<p>Extension-authors would be able to define custom filtersets for
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other users to use.</p>
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<p>A possible call to select a filterset would be:</p>
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<pre>$config->set('HTML', 'Filterset', 'Rich');</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 filtersets, there are various <strong>modes</strong> of operation.
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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, will definitely affect the output.
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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>Deprecated elements and attributes will be transformed into
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standards-compliant alternatives when explicitly disallowed. For
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example, in the XHTML 1.0 Strict doctype, a <code>center</code>
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tag would be turned into a <code>div</code> with the CSS property
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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 tag would be preserved. This mode is on by default.</dd>
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<dt>Correctional</dt>
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<dd>Deprecated elements and attributes will be transformed into
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standards-compliant alternatives whenever possible. Referring
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back to the previous example, the <code>center</code> tag would
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be transformed in both cases. However, tags without a
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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. This mode is on by default. It may have
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various levels of operation.</dd>
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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>$config->set('HTML', 'Mode', array('correctional', 'lenient'));</pre>
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<p>If modes have extra parameters, a hash might work well:</p>
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<p>If modes have extra parameters, a hash is necessary:</p>
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<pre>$config->set('HTML', 'Mode', array(
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'correctional' => 9, // strongest level
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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 possibly be wrapped up with the filterset declaration:</p>
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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>$config->set('HTML', 'Filterset', 'Rich: correctional, lenient');</pre>
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<pre>$config->setDoctype('XHTML Transitional 1.0', '+correctional[center,a.name] -lenient');</pre>
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<p>Further investigation in this field is necessary.</p>
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<p>With regards to the various levels of operation conjectured in the
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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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tag but not the <code>u</code> tag, both of which are deprecated.
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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 Tags / Attributes / Modules</h3>
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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, tags and
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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/tag/attribute selection configuration directives were
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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>$config->setAllowedHTML('a[href,title],em,p,blockquote');</pre>
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<p>We currently support a separated interface, which also must be preserved:</p>
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<pre>$config->set('HTML', 'AllowedTags', 'a,em,p,blockquote');
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$config->set('HTML', 'AllowedAttributes', 'a.href,a.title');</pre>
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<pre>$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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@ -178,13 +172,16 @@ $config->setAllowedHTML('Hypertext,Text,Lists');</pre>
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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> tag to the not-so-safe <code>h1</code>
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tag). How do we make this still a viable solution?</p>
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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 tags by the
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case of their first letter. While XML distinguishes between lower and uppercase
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letters, in practice, most well-known XML languages use only lower-case
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tag names for sake of consistency.</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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@ -202,6 +199,89 @@ for selecting a filterset. Possibility:</p>
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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>
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