diff --git a/extlib/HTMLPurifier/HTMLPurifier.autoload-legacy.php b/extlib/HTMLPurifier/HTMLPurifier.autoload-legacy.php
new file mode 100644
index 0000000000..c271cd1588
--- /dev/null
+++ b/extlib/HTMLPurifier/HTMLPurifier.autoload-legacy.php
@@ -0,0 +1,15 @@
+<?php
+
+/**
+ * @file
+ * Legacy autoloader for systems lacking spl_autoload_register
+ *
+ * Must be separate to prevent deprecation warning on PHP 7.2
+ */
+
+function __autoload($class)
+{
+    return HTMLPurifier_Bootstrap::autoload($class);
+}
+
+// vim: et sw=4 sts=4
diff --git a/extlib/HTMLPurifier/HTMLPurifier.autoload.php b/extlib/HTMLPurifier/HTMLPurifier.autoload.php
index c3ea67e814..9d8d299261 100644
--- a/extlib/HTMLPurifier/HTMLPurifier.autoload.php
+++ b/extlib/HTMLPurifier/HTMLPurifier.autoload.php
@@ -14,10 +14,7 @@ if (function_exists('spl_autoload_register') && function_exists('spl_autoload_un
         spl_autoload_register('__autoload');
     }
 } elseif (!function_exists('__autoload')) {
-    function __autoload($class)
-    {
-        return HTMLPurifier_Bootstrap::autoload($class);
-    }
+    require dirname(__FILE__) . '/HTMLPurifier.autoload-legacy.php';
 }
 
 if (ini_get('zend.ze1_compatibility_mode')) {
diff --git a/extlib/HTMLPurifier/HTMLPurifier.includes.php b/extlib/HTMLPurifier/HTMLPurifier.includes.php
index e8bce5c850..321bdc5661 100644
--- a/extlib/HTMLPurifier/HTMLPurifier.includes.php
+++ b/extlib/HTMLPurifier/HTMLPurifier.includes.php
@@ -7,7 +7,7 @@
  * primary concern and you are using an opcode cache. PLEASE DO NOT EDIT THIS
  * FILE, changes will be overwritten the next time the script is run.
  *
- * @version 4.9.3
+ * @version 4.10.0
  *
  * @warning
  *      You must *not* include any other HTML Purifier files before this file,
diff --git a/extlib/HTMLPurifier/HTMLPurifier.php b/extlib/HTMLPurifier/HTMLPurifier.php
index b4605ebc6e..bada5188b4 100644
--- a/extlib/HTMLPurifier/HTMLPurifier.php
+++ b/extlib/HTMLPurifier/HTMLPurifier.php
@@ -19,7 +19,7 @@
  */
 
 /*
-    HTML Purifier 4.9.3 - Standards Compliant HTML Filtering
+    HTML Purifier 4.10.0 - Standards Compliant HTML Filtering
     Copyright (C) 2006-2008 Edward Z. Yang
 
     This library is free software; you can redistribute it and/or
@@ -58,12 +58,12 @@ class HTMLPurifier
      * Version of HTML Purifier.
      * @type string
      */
-    public $version = '4.9.3';
+    public $version = '4.10.0';
 
     /**
      * Constant with version of HTML Purifier.
      */
-    const VERSION = '4.9.3';
+    const VERSION = '4.10.0';
 
     /**
      * Global configuration object.
diff --git a/extlib/HTMLPurifier/HTMLPurifier/AttrDef/URI/Host.php b/extlib/HTMLPurifier/HTMLPurifier/AttrDef/URI/Host.php
index 3b4d186743..e54a3344a7 100644
--- a/extlib/HTMLPurifier/HTMLPurifier/AttrDef/URI/Host.php
+++ b/extlib/HTMLPurifier/HTMLPurifier/AttrDef/URI/Host.php
@@ -97,7 +97,7 @@ class HTMLPurifier_AttrDef_URI_Host extends HTMLPurifier_AttrDef
 
         // PHP 5.3 and later support this functionality natively
         if (function_exists('idn_to_ascii')) {
-            $string = idn_to_ascii($string);
+            $string = idn_to_ascii($string, IDNA_NONTRANSITIONAL_TO_ASCII, INTL_IDNA_VARIANT_UTS46);
 
         // If we have Net_IDNA2 support, we can support IRIs by
         // punycoding them. (This is the most portable thing to do,
diff --git a/extlib/HTMLPurifier/HTMLPurifier/Config.php b/extlib/HTMLPurifier/HTMLPurifier/Config.php
index 3648364b30..f37cf3713d 100644
--- a/extlib/HTMLPurifier/HTMLPurifier/Config.php
+++ b/extlib/HTMLPurifier/HTMLPurifier/Config.php
@@ -21,7 +21,7 @@ class HTMLPurifier_Config
      * HTML Purifier's version
      * @type string
      */
-    public $version = '4.9.3';
+    public $version = '4.10.0';
 
     /**
      * Whether or not to automatically finalize
diff --git a/extlib/HTMLPurifier/HTMLPurifier/DefinitionCache/Serializer.php b/extlib/HTMLPurifier/HTMLPurifier/DefinitionCache/Serializer.php
index 952e48d470..b82c6bb201 100644
--- a/extlib/HTMLPurifier/HTMLPurifier/DefinitionCache/Serializer.php
+++ b/extlib/HTMLPurifier/HTMLPurifier/DefinitionCache/Serializer.php
@@ -217,9 +217,14 @@ class HTMLPurifier_DefinitionCache_Serializer extends HTMLPurifier_DefinitionCac
         $directory = $this->generateDirectoryPath($config);
         $chmod = $config->get('Cache.SerializerPermissions');
         if ($chmod === null) {
-            // TODO: This races
-            if (is_dir($directory)) return true;
-            return mkdir($directory);
+            if (!@mkdir($directory) && !is_dir($directory)) {
+                trigger_error(
+                    'Could not create directory ' . $directory . '',
+                    E_USER_WARNING
+                );
+                return false;
+            }
+            return true;
         }
         if (!is_dir($directory)) {
             $base = $this->generateBaseDirectoryPath($config);
@@ -233,7 +238,7 @@ class HTMLPurifier_DefinitionCache_Serializer extends HTMLPurifier_DefinitionCac
             } elseif (!$this->_testPermissions($base, $chmod)) {
                 return false;
             }
-            if (!mkdir($directory, $chmod)) {
+            if (!@mkdir($directory, $chmod) && !is_dir($directory)) {
                 trigger_error(
                     'Could not create directory ' . $directory . '',
                     E_USER_WARNING
diff --git a/extlib/HTMLPurifier/HTMLPurifier/Injector.php b/extlib/HTMLPurifier/HTMLPurifier/Injector.php
index 5060eef9e2..116b470c37 100644
--- a/extlib/HTMLPurifier/HTMLPurifier/Injector.php
+++ b/extlib/HTMLPurifier/HTMLPurifier/Injector.php
@@ -157,11 +157,13 @@ abstract class HTMLPurifier_Injector
             return false;
         }
         // check for exclusion
-        for ($i = count($this->currentNesting) - 2; $i >= 0; $i--) {
-            $node = $this->currentNesting[$i];
-            $def  = $this->htmlDefinition->info[$node->name];
-            if (isset($def->excludes[$name])) {
-                return false;
+        if (!empty($this->currentNesting)) {
+            for ($i = count($this->currentNesting) - 2; $i >= 0; $i--) {
+                $node = $this->currentNesting[$i];
+                $def  = $this->htmlDefinition->info[$node->name];
+                if (isset($def->excludes[$name])) {
+                    return false;
+                }
             }
         }
         return true;
diff --git a/extlib/HTMLPurifier/HTMLPurifier/Length.php b/extlib/HTMLPurifier/HTMLPurifier/Length.php
index bbfbe6624d..e70da55a92 100644
--- a/extlib/HTMLPurifier/HTMLPurifier/Length.php
+++ b/extlib/HTMLPurifier/HTMLPurifier/Length.php
@@ -26,12 +26,14 @@ class HTMLPurifier_Length
     protected $isValid;
 
     /**
-     * Array Lookup array of units recognized by CSS 2.1
+     * Array Lookup array of units recognized by CSS 3
      * @type array
      */
     protected static $allowedUnits = array(
         'em' => true, 'ex' => true, 'px' => true, 'in' => true,
-        'cm' => true, 'mm' => true, 'pt' => true, 'pc' => true
+        'cm' => true, 'mm' => true, 'pt' => true, 'pc' => true,
+        'ch' => true, 'rem' => true, 'vw' => true, 'vh' => true,
+        'vmin' => true, 'vmax' => true
     );
 
     /**
diff --git a/extlib/HTMLPurifier/HTMLPurifier/Lexer/DOMLex.php b/extlib/HTMLPurifier/HTMLPurifier/Lexer/DOMLex.php
index 22ab5820c5..6238a99e34 100644
--- a/extlib/HTMLPurifier/HTMLPurifier/Lexer/DOMLex.php
+++ b/extlib/HTMLPurifier/HTMLPurifier/Lexer/DOMLex.php
@@ -126,6 +126,41 @@ class HTMLPurifier_Lexer_DOMLex extends HTMLPurifier_Lexer
         } while ($level > 0);
     }
 
+    /**
+     * Portably retrieve the tag name of a node; deals with older versions
+     * of libxml like 2.7.6
+     * @param DOMNode $node
+     */
+    protected function getTagName($node)
+    {
+        if (property_exists($node, 'tagName')) {
+            return $node->tagName;
+        } else if (property_exists($node, 'nodeName')) {
+            return $node->nodeName;
+        } else if (property_exists($node, 'localName')) {
+            return $node->localName;
+        }
+        return null;
+    }
+
+    /**
+     * Portably retrieve the data of a node; deals with older versions
+     * of libxml like 2.7.6
+     * @param DOMNode $node
+     */
+    protected function getData($node)
+    {
+        if (property_exists($node, 'data')) {
+            return $node->data;
+        } else if (property_exists($node, 'nodeValue')) {
+            return $node->nodeValue;
+        } else if (property_exists($node, 'textContent')) {
+            return $node->textContent;
+        }
+        return null;
+    }
+
+
     /**
      * @param DOMNode $node DOMNode to be tokenized.
      * @param HTMLPurifier_Token[] $tokens   Array-list of already tokenized tokens.
@@ -141,7 +176,10 @@ class HTMLPurifier_Lexer_DOMLex extends HTMLPurifier_Lexer
         // but we're not getting the character reference nodes because
         // those should have been preprocessed
         if ($node->nodeType === XML_TEXT_NODE) {
-            $tokens[] = $this->factory->createText($node->data);
+            $data = $this->getData($node); // Handle variable data property
+            if ($data !== null) {
+              $tokens[] = $this->factory->createText($data);
+            }
             return false;
         } elseif ($node->nodeType === XML_CDATA_SECTION_NODE) {
             // undo libxml's special treatment of <script> and <style> tags
@@ -171,21 +209,20 @@ class HTMLPurifier_Lexer_DOMLex extends HTMLPurifier_Lexer
             // not-well tested: there may be other nodes we have to grab
             return false;
         }
-
         $attr = $node->hasAttributes() ? $this->transformAttrToAssoc($node->attributes) : array();
-
+        $tag_name = $this->getTagName($node); // Handle variable tagName property
+        if (empty($tag_name)) {
+            return (bool) $node->childNodes->length;
+        }
         // We still have to make sure that the element actually IS empty
         if (!$node->childNodes->length) {
             if ($collect) {
-                $tokens[] = $this->factory->createEmpty($node->tagName, $attr);
+                $tokens[] = $this->factory->createEmpty($tag_name, $attr);
             }
             return false;
         } else {
             if ($collect) {
-                $tokens[] = $this->factory->createStart(
-                    $tag_name = $node->tagName, // somehow, it get's dropped
-                    $attr
-                );
+                $tokens[] = $this->factory->createStart($tag_name, $attr);
             }
             return true;
         }
@@ -197,10 +234,10 @@ class HTMLPurifier_Lexer_DOMLex extends HTMLPurifier_Lexer
      */
     protected function createEndNode($node, &$tokens)
     {
-        $tokens[] = $this->factory->createEnd($node->tagName);
+        $tag_name = $this->getTagName($node); // Handle variable tagName property
+        $tokens[] = $this->factory->createEnd($tag_name);
     }
 
-
     /**
      * Converts a DOMNamedNodeMap of DOMAttr objects into an assoc array.
      *
diff --git a/extlib/HTMLPurifier/HTMLPurifier/Lexer/PH5P.php b/extlib/HTMLPurifier/HTMLPurifier/Lexer/PH5P.php
index 0b452d17fc..72476ddf32 100644
--- a/extlib/HTMLPurifier/HTMLPurifier/Lexer/PH5P.php
+++ b/extlib/HTMLPurifier/HTMLPurifier/Lexer/PH5P.php
@@ -1507,7 +1507,7 @@ class HTML5
                 $entity = $this->character($start, $this->char);
                 $cond = strlen($e_name) > 0;
 
-                // The rest of the parsing happens bellow.
+                // The rest of the parsing happens below.
                 break;
 
             // Anything else
@@ -1535,7 +1535,7 @@ class HTML5
                 }
 
                 $cond = isset($entity);
-                // The rest of the parsing happens bellow.
+                // The rest of the parsing happens below.
                 break;
         }
 
diff --git a/extlib/HTMLPurifier/VERSION b/extlib/HTMLPurifier/VERSION
index e94f14fa9e..2da4316236 100644
--- a/extlib/HTMLPurifier/VERSION
+++ b/extlib/HTMLPurifier/VERSION
@@ -1 +1 @@
-4.9.3
\ No newline at end of file
+4.10.0