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/AttrDef/HTML/Length.php

@@ -0,0 +1,41 @@
+<?php
+
+/**
+ * Validates the HTML type length (not to be confused with CSS's length).
+ *
+ * This accepts integer pixels or percentages as lengths for certain
+ * HTML attributes.
+ */
+
+class HTMLPurifier_AttrDef_HTML_Length extends HTMLPurifier_AttrDef_HTML_Pixels
+{
+
+    public function validate($string, $config, $context) {
+
+        $string = trim($string);
+        if ($string === '') return false;
+
+        $parent_result = parent::validate($string, $config, $context);
+        if ($parent_result !== false) return $parent_result;
+
+        $length = strlen($string);
+        $last_char = $string[$length - 1];
+
+        if ($last_char !== '%') return false;
+
+        $points = substr($string, 0, $length - 1);
+
+        if (!is_numeric($points)) return false;
+
+        $points = (int) $points;
+
+        if ($points < 0) return '0%';
+        if ($points > 100) return '100%';
+
+        return ((string) $points) . '%';
+
+    }
+
+}
+
+// vim: et sw=4 sts=4