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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"><head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<meta name="description" content="Tutorial for customizing HTML Purifier's tag and attribute sets." />
<link rel="stylesheet" type="text/css" href="style.css" />
<title>Customize - HTML Purifier</title>
</head><body>
<h1 class="subtitled">Customize!</h1>
<div class="subtitle">HTML Purifier is a Swiss-Army Knife</div>
<div id="filing">Filed under End-User</div>
<div id="index">Return to the <a href="index.html">index</a>.</div>
<div id="home"><a href="http://htmlpurifier.org/">HTML Purifier</a> End-User Documentation</div>
<p>
HTML Purifier has this quirk where if you try to allow certain elements or
attributes, HTML Purifier will tell you that it's not supported, and that
you should go to the forums to find out how to implement it. Well, this
document is how to implement elements and attributes which HTML Purifier
doesn't support out of the box.
</p>
<h2>Is it necessary?</h2>
<p>
Before we even write any code, it is paramount to consider whether or
not the code we're writing is necessary or not. HTML Purifier, by default,
contains a large set of elements and attributes: large enough so that
<em>any</em> element or attribute in XHTML 1.0 or 1.1 (and its HTML variants)
that can be safely used by the general public is implemented.
</p>
<p>
So what needs to be implemented? (Feel free to skip this section if
you know what you want).
</p>
<h3>XHTML 1.0</h3>
<p>
All of the modules listed below are based off of the
<a href="http://www.w3.org/TR/2001/REC-xhtml-modularization-20010410/abstract_modules.html#sec_5.2.">modularization of
XHTML</a>, which, while technically for XHTML 1.1, is quite a useful
resource.
</p>
<ul>
<li>Structure</li>
<li>Frames</li>
<li>Applets (deprecated)</li>
<li>Forms</li>
<li>Image maps</li>
<li>Objects</li>
<li>Frames</li>
<li>Events</li>
<li>Meta-information</li>
<li>Style sheets</li>
<li>Link (not hypertext)</li>
<li>Base</li>
<li>Name</li>
</ul>
<p>
If you don't recognize it, you probably don't need it. But the curious
can look all of these modules up in the above-mentioned document. Note
that inline scripting comes packaged with HTML Purifier (more on this
later).
</p>
<h3>XHTML 1.1</h3>
<p>
As of HTMLPurifier 2.1.0, we have implemented the
<a href="http://www.w3.org/TR/2001/REC-ruby-20010531/">Ruby module</a>,
which defines a set of tags
for publishing short annotations for text, used mostly in Japanese
and Chinese school texts, but applicable for positioning any text (not
limited to translations) above or below other corresponding text.
</p>
<h3>HTML 5</h3>
<p>
<a href="http://www.whatwg.org/specs/web-apps/current-work/">HTML 5</a>
is a fork of HTML 4.01 by WHATWG, who believed that XHTML 2.0 was headed
in the wrong direction. It too is a working draft, and may change
drastically before publication, but it should be noted that the
<code>canvas</code> tag has been implemented by many browser vendors.
</p>
<h3>Proprietary</h3>
<p>
There are a number of proprietary tags still in the wild. Many of them
have been documented in <a href="ref-proprietary-tags.txt">ref-proprietary-tags.txt</a>,
but there is currently no implementation for any of them.
</p>
<h3>Extensions</h3>
<p>
There are also a number of other XML languages out there that can
be embedded in HTML documents: two of the most popular are MathML and
SVG, and I frequently get requests to implement these. But they are
expansive, comprehensive specifications, and it would take far too long
to implement them <em>correctly</em> (most systems I've seen go as far
as whitelisting tags and no further; come on, what about nesting!)
</p>
<p>
Word of warning: HTML Purifier is currently <em>not</em> namespace
aware.
</p>
<h2>Giving back</h2>
<p>
As you may imagine from the details above (don't be abashed if you didn't
read it all: a glance over would have done), there's quite a bit that
HTML Purifier doesn't implement. Recent architectural changes have
allowed HTML Purifier to implement elements and attributes that are not
safe! Don't worry, they won't be activated unless you set %HTML.Trusted
to true, but they certainly help out users who need to put, say, forms
on their page and don't want to go through the trouble of reading this
and implementing it themself.
</p>
<p>
So any of the above that you implement for your own application could
help out some other poor sap on the other side of the globe. Help us
out, and send back code so that it can be hammered into a module and
released with the core. Any code would be greatly appreciated!
</p>
<h2>And now...</h2>
<p>
Enough philosophical talk, time for some code:
</p>
<pre>$config = HTMLPurifier_Config::createDefault();
$config->set('HTML.DefinitionID', 'enduser-customize.html tutorial');
$config->set('HTML.DefinitionRev', 1);
if ($def = $config->maybeGetRawHTMLDefinition()) {
// our code will go here
}</pre>
<p>
Assuming that HTML Purifier has already been properly loaded (hint:
include <code>HTMLPurifier.auto.php</code>), this code will set up
the environment that you need to start customizing the HTML definition.
What's going on?
</p>
<ul>
<li>
The first three lines are regular configuration code:
<ul>
<li>
%HTML.DefinitionID is set to a unique identifier for your
custom HTML definition. This prevents it from clobbering
other custom definitions on the same installation.
</li>
<li>
%HTML.DefinitionRev is a revision integer of your HTML
definition. Because HTML definitions are cached, you'll need
to increment this whenever you make a change in order to flush
the cache.
</li>
</ul>
</li>
<li>
The fourth line retrieves a raw <code>HTMLPurifier_HTMLDefinition</code>
object that we will be tweaking. Interestingly enough, we have
placed it in an if block: this is because
<code>maybeGetRawHTMLDefinition</code>, as its name suggests, may
return a NULL, in which case we should skip doing any
initialization. This, in fact, will correspond to when our fully
customized object is already in the cache.
</li>
</ul>
<h2>Turn off caching</h2>
<p>
To make development easier, we're going to temporarily turn off
definition caching:
</p>
<pre>$config = HTMLPurifier_Config::createDefault();
$config->set('HTML.DefinitionID', 'enduser-customize.html tutorial');
$config->set('HTML.DefinitionRev', 1);
<strong>$config->set('Cache.DefinitionImpl', null); // TODO: remove this later!</strong>
$def = $config->getHTMLDefinition(true);</pre>
<p>
A few things should be mentioned about the caching mechanism before
we move on. For performance reasons, HTML Purifier caches generated
<code>HTMLPurifier_Definition</code> objects in serialized files
stored (by default) in <code>library/HTMLPurifier/DefinitionCache/Serializer</code>.
A lot of processing is done in order to create these objects, so it
makes little sense to repeat the same processing over and over again
whenever HTML Purifier is called.
</p>
<p>
In order to identify a cache entry, HTML Purifier uses three variables:
the library's version number, the value of %HTML.DefinitionRev and
a serial of relevant configuration. Whenever any of these changes,
a new HTML definition is generated. Notice that there is no way
for the definition object to track changes to customizations: here, it
is up to you to supply appropriate information to DefinitionID and
DefinitionRev.
</p>
<h2 id="addAttribute">Add an attribute</h2>
<p>
For this example, we're going to implement the <code>target</code> attribute found
on <code>a</
|