Escape story fields and clean story HTML with HTML Purifier.

Add HTML Purifier 4.19.1. Stories are purified when they are saved and
when they are shown.

lib/htmlpurifier-4.19.1/library/HTMLPurifier/AttrDef/HTML/ContentEditable.php

@@ -0,0 +1,16 @@
+<?php
+
+class HTMLPurifier_AttrDef_HTML_ContentEditable extends HTMLPurifier_AttrDef
+{
+    public function validate($string, $config, $context)
+    {
+        $allowed = array('false');
+        if ($config->get('HTML.Trusted')) {
+            $allowed = array('', 'true', 'false');
+        }
+
+        $enum = new HTMLPurifier_AttrDef_Enum($allowed);
+
+        return $enum->validate($string, $config, $context);
+    }
+}