Add website to client repository

Closes #1567

The main reason I'm not simply merging Annika's PR is because this
way makes it clearer that I'm taking responsibility for all this
code, that it's mostly code I wrote, and also because it makes it
easier to ensure that none of the files have been changed.

(Not that I don't personally trust Annika, but I have something
resembling an obligation to users not to expose them to risks based
on personal trust.)

website/lib/htmlpurifier/HTMLPurifier/ChildDef.php

@@ -0,0 +1,48 @@
+<?php
+
+/**
+ * Defines allowed child nodes and validates tokens against it.
+ */
+abstract class HTMLPurifier_ChildDef
+{
+    /**
+     * Type of child definition, usually right-most part of class name lowercase.
+     * Used occasionally in terms of context.
+     */
+    public $type;
+
+    /**
+     * Bool that indicates whether or not an empty array of children is okay
+     *
+     * This is necessary for redundant checking when changes affecting
+     * a child node may cause a parent node to now be disallowed.
+     */
+    public $allow_empty;
+
+    /**
+     * Lookup array of all elements that this definition could possibly allow
+     */
+    public $elements = array();
+
+    /**
+     * Get lookup of tag names that should not close this element automatically.
+     * All other elements will do so.
+     */
+    public function getAllowedElements($config) {
+        return $this->elements;
+    }
+
+    /**
+     * Validates nodes according to definition and returns modification.
+     *
+     * @param $tokens_of_children Array of HTMLPurifier_Token
+     * @param $config HTMLPurifier_Config object
+     * @param $context HTMLPurifier_Context object
+     * @return bool true to leave nodes as is
+     * @return bool false to remove parent node
+     * @return array of replacement child tokens
+     */
+    abstract public function validateChildren($tokens_of_children, $config, $context);
+}
+
+// vim: et sw=4 sts=4