diff --git a/lib/htmlpurifier/HTMLPurifier.php b/lib/htmlpurifier/HTMLPurifier.php
index 2177fc85172..26f061276f7 100644
--- a/lib/htmlpurifier/HTMLPurifier.php
+++ b/lib/htmlpurifier/HTMLPurifier.php
@@ -19,7 +19,7 @@
  */
 
 /*
-    HTML Purifier 4.14.0 - Standards Compliant HTML Filtering
+    HTML Purifier 4.15.0 - 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 = '4.14.0';
+    public $version = '4.15.0';
 
     /**
      * Constant with version of HTML Purifier.
      */
-    const VERSION = '4.14.0';
+    const VERSION = '4.15.0';
 
     /**
      * Global configuration object.
diff --git a/lib/htmlpurifier/HTMLPurifier.safe-includes.php b/lib/htmlpurifier/HTMLPurifier.safe-includes.php
index a3261f8a327..94543f593de 100644
--- a/lib/htmlpurifier/HTMLPurifier.safe-includes.php
+++ b/lib/htmlpurifier/HTMLPurifier.safe-includes.php
@@ -101,6 +101,7 @@ require_once $__dir . '/HTMLPurifier/AttrDef/HTML/Bool.php';
 require_once $__dir . '/HTMLPurifier/AttrDef/HTML/Nmtokens.php';
 require_once $__dir . '/HTMLPurifier/AttrDef/HTML/Class.php';
 require_once $__dir . '/HTMLPurifier/AttrDef/HTML/Color.php';
+require_once $__dir . '/HTMLPurifier/AttrDef/HTML/ContentEditable.php';
 require_once $__dir . '/HTMLPurifier/AttrDef/HTML/FrameTarget.php';
 require_once $__dir . '/HTMLPurifier/AttrDef/HTML/ID.php';
 require_once $__dir . '/HTMLPurifier/AttrDef/HTML/Pixels.php';
diff --git a/lib/htmlpurifier/HTMLPurifier/AttrDef/HTML/ContentEditable.php b/lib/htmlpurifier/HTMLPurifier/AttrDef/HTML/ContentEditable.php
new file mode 100644
index 00000000000..5b03d3e3785
--- /dev/null
+++ b/lib/htmlpurifier/HTMLPurifier/AttrDef/HTML/ContentEditable.php
@@ -0,0 +1,16 @@
+<?php
+
+class HTMLPurifier_AttrDef_HTML_ContentEditable extends HTMLPurifier_AttrDef
+{
+    public function validate($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);
+    }
+}
diff --git a/lib/htmlpurifier/HTMLPurifier/AttrTransform/NameSync.php b/lib/htmlpurifier/HTMLPurifier/AttrTransform/NameSync.php
index 36079b786ff..5a1fdbbfcc8 100644
--- a/lib/htmlpurifier/HTMLPurifier/AttrTransform/NameSync.php
+++ b/lib/htmlpurifier/HTMLPurifier/AttrTransform/NameSync.php
@@ -8,6 +8,11 @@
 class HTMLPurifier_AttrTransform_NameSync extends HTMLPurifier_AttrTransform
 {
 
+    /**
+     * @type HTMLPurifier_AttrDef_HTML_ID
+     */
+    public $idDef;
+
     public function __construct()
     {
         $this->idDef = new HTMLPurifier_AttrDef_HTML_ID();
diff --git a/lib/htmlpurifier/HTMLPurifier/AttrTransform/SafeParam.php b/lib/htmlpurifier/HTMLPurifier/AttrTransform/SafeParam.php
index 1143b4b4930..1033106b387 100644
--- a/lib/htmlpurifier/HTMLPurifier/AttrTransform/SafeParam.php
+++ b/lib/htmlpurifier/HTMLPurifier/AttrTransform/SafeParam.php
@@ -24,6 +24,11 @@ class HTMLPurifier_AttrTransform_SafeParam extends HTMLPurifier_AttrTransform
      */
     private $uri;
 
+    /**
+     * @type HTMLPurifier_AttrDef_Enum
+     */
+    public $wmode;
+
     public function __construct()
     {
         $this->uri = new HTMLPurifier_AttrDef_URI(true); // embedded
diff --git a/lib/htmlpurifier/HTMLPurifier/AttrTypes.php b/lib/htmlpurifier/HTMLPurifier/AttrTypes.php
index 3b70520b6ad..e4429e86d87 100644
--- a/lib/htmlpurifier/HTMLPurifier/AttrTypes.php
+++ b/lib/htmlpurifier/HTMLPurifier/AttrTypes.php
@@ -41,6 +41,7 @@ class HTMLPurifier_AttrTypes
         $this->info['IAlign']   = self::makeEnum('top,middle,bottom,left,right');
         $this->info['LAlign']   = self::makeEnum('top,bottom,left,right');
         $this->info['FrameTarget'] = new HTMLPurifier_AttrDef_HTML_FrameTarget();
+        $this->info['ContentEditable'] = new HTMLPurifier_AttrDef_HTML_ContentEditable();
 
         // unimplemented aliases
         $this->info['ContentType'] = new HTMLPurifier_AttrDef_Text();
diff --git a/lib/htmlpurifier/HTMLPurifier/ChildDef/List.php b/lib/htmlpurifier/HTMLPurifier/ChildDef/List.php
index 4fc70e0efa7..3d584e72712 100644
--- a/lib/htmlpurifier/HTMLPurifier/ChildDef/List.php
+++ b/lib/htmlpurifier/HTMLPurifier/ChildDef/List.php
@@ -22,6 +22,8 @@ class HTMLPurifier_ChildDef_List extends HTMLPurifier_ChildDef
     // XXX: This whole business with 'wrap' is all a bit unsatisfactory
     public $elements = array('li' => true, 'ul' => true, 'ol' => true);
 
+    public $whitespace;
+
     /**
      * @param array $children
      * @param HTMLPurifier_Config $config
diff --git a/lib/htmlpurifier/HTMLPurifier/Config.php b/lib/htmlpurifier/HTMLPurifier/Config.php
index 16a6b322b5e..797d2687792 100644
--- a/lib/htmlpurifier/HTMLPurifier/Config.php
+++ b/lib/htmlpurifier/HTMLPurifier/Config.php
@@ -21,7 +21,7 @@ class HTMLPurifier_Config
      * HTML Purifier's version
      * @type string
      */
-    public $version = '4.14.0';
+    public $version = '4.15.0';
 
     /**
      * Whether or not to automatically finalize
diff --git a/lib/htmlpurifier/HTMLPurifier/ElementDef.php b/lib/htmlpurifier/HTMLPurifier/ElementDef.php
index d5311cedcf3..57cfd2bb080 100644
--- a/lib/htmlpurifier/HTMLPurifier/ElementDef.php
+++ b/lib/htmlpurifier/HTMLPurifier/ElementDef.php
@@ -176,7 +176,7 @@ class HTMLPurifier_ElementDef
 
         if (!empty($def->content_model)) {
             $this->content_model =
-                str_replace("#SUPER", $this->content_model, $def->content_model);
+                str_replace("#SUPER", (string)$this->content_model, $def->content_model);
             $this->child = false;
         }
         if (!empty($def->content_model_type)) {
diff --git a/lib/htmlpurifier/HTMLPurifier/Encoder.php b/lib/htmlpurifier/HTMLPurifier/Encoder.php
index 40a24266a46..d4791cc1b61 100644
--- a/lib/htmlpurifier/HTMLPurifier/Encoder.php
+++ b/lib/htmlpurifier/HTMLPurifier/Encoder.php
@@ -398,8 +398,8 @@ class HTMLPurifier_Encoder
             // characters to their true byte-wise ASCII/UTF-8 equivalents.
             $str = strtr($str, self::testEncodingSupportsASCII($encoding));
             return $str;
-        } elseif ($encoding === 'iso-8859-1') {
-            $str = utf8_encode($str);
+        } elseif ($encoding === 'iso-8859-1' && function_exists('mb_convert_encoding')) {
+            $str = mb_convert_encoding($str, 'UTF-8', 'ISO-8859-1');
             return $str;
         }
         $bug = HTMLPurifier_Encoder::testIconvTruncateBug();
@@ -450,8 +450,8 @@ class HTMLPurifier_Encoder
             // Normal stuff
             $str = self::iconv('utf-8', $encoding . '//IGNORE', $str);
             return $str;
-        } elseif ($encoding === 'iso-8859-1') {
-            $str = utf8_decode($str);
+        } elseif ($encoding === 'iso-8859-1' && function_exists('mb_convert_encoding')) {
+            $str = mb_convert_encoding($str, 'ISO-8859-1', 'UTF-8');
             return $str;
         }
         trigger_error('Encoding not supported', E_USER_ERROR);
diff --git a/lib/htmlpurifier/HTMLPurifier/HTMLModule/CommonAttributes.php b/lib/htmlpurifier/HTMLPurifier/HTMLModule/CommonAttributes.php
index a96ab1bef11..7220c14cc7c 100644
--- a/lib/htmlpurifier/HTMLPurifier/HTMLModule/CommonAttributes.php
+++ b/lib/htmlpurifier/HTMLPurifier/HTMLModule/CommonAttributes.php
@@ -17,6 +17,7 @@ class HTMLPurifier_HTMLModule_CommonAttributes extends HTMLPurifier_HTMLModule
             'class' => 'Class',
             'id' => 'ID',
             'title' => 'CDATA',
+            'contenteditable' => 'ContentEditable',
         ),
         'Lang' => array(),
         'I18N' => array(
diff --git a/lib/htmlpurifier/HTMLPurifier/Injector/RemoveSpansWithoutAttributes.php b/lib/htmlpurifier/HTMLPurifier/Injector/RemoveSpansWithoutAttributes.php
index 9ee7aa84d71..42d51444740 100644
--- a/lib/htmlpurifier/HTMLPurifier/Injector/RemoveSpansWithoutAttributes.php
+++ b/lib/htmlpurifier/HTMLPurifier/Injector/RemoveSpansWithoutAttributes.php
@@ -31,6 +31,16 @@ class HTMLPurifier_Injector_RemoveSpansWithoutAttributes extends HTMLPurifier_In
      */
     private $context;
 
+    /**
+     * @type SplObjectStorage
+     */
+    private $markForDeletion;
+
+    public function __construct()
+    {
+        $this->markForDeletion = new SplObjectStorage();
+    }
+
     public function prepare($config, $context)
     {
         $this->attrValidator = new HTMLPurifier_AttrValidator();
@@ -64,7 +74,7 @@ class HTMLPurifier_Injector_RemoveSpansWithoutAttributes extends HTMLPurifier_In
 
         if ($current instanceof HTMLPurifier_Token_End && $current->name === 'span') {
             // Mark closing span tag for deletion
-            $current->markForDeletion = true;
+            $this->markForDeletion->attach($current);
             // Delete open span tag
             $token = false;
         }
@@ -75,7 +85,8 @@ class HTMLPurifier_Injector_RemoveSpansWithoutAttributes extends HTMLPurifier_In
      */
     public function handleEnd(&$token)
     {
-        if ($token->markForDeletion) {
+        if ($this->markForDeletion->contains($token)) {
+            $this->markForDeletion->detach($token);
             $token = false;
         }
     }
diff --git a/lib/htmlpurifier/HTMLPurifier/Length.php b/lib/htmlpurifier/HTMLPurifier/Length.php
index e70da55a923..b6ea12345da 100644
--- a/lib/htmlpurifier/HTMLPurifier/Length.php
+++ b/lib/htmlpurifier/HTMLPurifier/Length.php
@@ -78,7 +78,7 @@ class HTMLPurifier_Length
         if ($this->n === '0' && $this->unit === false) {
             return true;
         }
-        if (!ctype_lower($this->unit)) {
+        if ($this->unit === false || !ctype_lower($this->unit)) {
             $this->unit = strtolower($this->unit);
         }
         if (!isset(HTMLPurifier_Length::$allowedUnits[$this->unit])) {
diff --git a/lib/htmlpurifier/HTMLPurifier/Lexer.php b/lib/htmlpurifier/HTMLPurifier/Lexer.php
index e9da3ed5e94..c21f364919c 100644
--- a/lib/htmlpurifier/HTMLPurifier/Lexer.php
+++ b/lib/htmlpurifier/HTMLPurifier/Lexer.php
@@ -48,6 +48,11 @@ class HTMLPurifier_Lexer
      */
     public $tracksLineNumbers = false;
 
+    /**
+     * @type HTMLPurifier_EntityParser
+     */
+    private $_entity_parser;
+
     // -- STATIC ----------------------------------------------------------
 
     /**
@@ -306,8 +311,8 @@ class HTMLPurifier_Lexer
     {
         // normalize newlines to \n
         if ($config->get('Core.NormalizeNewlines')) {
-            $html = str_replace("\r\n", "\n", $html);
-            $html = str_replace("\r", "\n", $html);
+            $html = str_replace("\r\n", "\n", (string)$html);
+            $html = str_replace("\r", "\n", (string)$html);
         }
 
         if ($config->get('HTML.Trusted')) {
diff --git a/lib/htmlpurifier/HTMLPurifier/Lexer/PH5P.php b/lib/htmlpurifier/HTMLPurifier/Lexer/PH5P.php
index 72476ddf32b..1564f283dc0 100644
--- a/lib/htmlpurifier/HTMLPurifier/Lexer/PH5P.php
+++ b/lib/htmlpurifier/HTMLPurifier/Lexer/PH5P.php
@@ -4410,7 +4410,7 @@ class HTML5TreeConstructer
 
         foreach ($token['attr'] as $attr) {
             if (!$el->hasAttribute($attr['name'])) {
-                $el->setAttribute($attr['name'], $attr['value']);
+                $el->setAttribute($attr['name'], (string)$attr['value']);
             }
         }
 
diff --git a/lib/htmlpurifier/HTMLPurifier/PropertyListIterator.php b/lib/htmlpurifier/HTMLPurifier/PropertyListIterator.php
index 15b330ea308..f68fc8c30fc 100644
--- a/lib/htmlpurifier/HTMLPurifier/PropertyListIterator.php
+++ b/lib/htmlpurifier/HTMLPurifier/PropertyListIterator.php
@@ -29,6 +29,7 @@ class HTMLPurifier_PropertyListIterator extends FilterIterator
     /**
      * @return bool
      */
+    #[\ReturnTypeWillChange]
     public function accept()
     {
         $key = $this->getInnerIterator()->key();
diff --git a/lib/htmlpurifier/HTMLPurifier/StringHash.php b/lib/htmlpurifier/HTMLPurifier/StringHash.php
index c07370197a9..c41ae3a76d5 100644
--- a/lib/htmlpurifier/HTMLPurifier/StringHash.php
+++ b/lib/htmlpurifier/HTMLPurifier/StringHash.php
@@ -20,6 +20,7 @@ class HTMLPurifier_StringHash extends ArrayObject
      * @param mixed $index
      * @return mixed
      */
+    #[\ReturnTypeWillChange]
     public function offsetGet($index)
     {
         $this->accessed[$index] = true;
diff --git a/lib/htmlpurifier/HTMLPurifier/URIFilter/HostBlacklist.php b/lib/htmlpurifier/HTMLPurifier/URIFilter/HostBlacklist.php
index a6645c17ee6..32197c0e614 100644
--- a/lib/htmlpurifier/HTMLPurifier/URIFilter/HostBlacklist.php
+++ b/lib/htmlpurifier/HTMLPurifier/URIFilter/HostBlacklist.php
@@ -35,7 +35,7 @@ class HTMLPurifier_URIFilter_HostBlacklist extends HTMLPurifier_URIFilter
     public function filter(&$uri, $config, $context)
     {
         foreach ($this->blacklist as $blacklisted_host_fragment) {
-            if (strpos($uri->host, $blacklisted_host_fragment) !== false) {
+            if ($uri->host !== null && strpos($uri->host, $blacklisted_host_fragment) !== false) {
                 return false;
             }
         }
diff --git a/lib/htmlpurifier/HTMLPurifier/URIFilter/Munge.php b/lib/htmlpurifier/HTMLPurifier/URIFilter/Munge.php
index 6e03315a17b..e1393deb739 100644
--- a/lib/htmlpurifier/HTMLPurifier/URIFilter/Munge.php
+++ b/lib/htmlpurifier/HTMLPurifier/URIFilter/Munge.php
@@ -100,11 +100,11 @@ class HTMLPurifier_URIFilter_Munge extends HTMLPurifier_URIFilter
         $string = $uri->toString();
         // always available
         $this->replace['%s'] = $string;
-        $this->replace['%r'] = $context->get('EmbeddedURI', true);
-        $token = $context->get('CurrentToken', true);
-        $this->replace['%n'] = $token ? $token->name : null;
-        $this->replace['%m'] = $context->get('CurrentAttr', true);
-        $this->replace['%p'] = $context->get('CurrentCSSProperty', true);
+        $this->replace['%r'] = $context->get('EmbeddedURI', true) ?: '';
+        $token = $context->get('CurrentToken', true) ?: '';
+        $this->replace['%n'] = $token ? $token->name : '';
+        $this->replace['%m'] = $context->get('CurrentAttr', true) ?: '';
+        $this->replace['%p'] = $context->get('CurrentCSSProperty', true) ?: '';
         // not always available
         if ($this->secretKey) {
             $this->replace['%t'] = hash_hmac("sha256", $string, $this->secretKey);
diff --git a/lib/thirdpartylibs.xml b/lib/thirdpartylibs.xml
index 1018325bc11..51f23e6d034 100644
--- a/lib/thirdpartylibs.xml
+++ b/lib/thirdpartylibs.xml
@@ -73,7 +73,7 @@
     <location>htmlpurifier</location>
     <name>HTML Purifier</name>
     <description>Filters HTML.</description>
-    <version>4.14.0</version>
+    <version>4.16.0</version>
     <license>LGPL</license>
     <licenseversion>2.1+</licenseversion>
     <repository>https://github.com/ezyang/htmlpurifier</repository>
diff --git a/lib/upgrade.txt b/lib/upgrade.txt
index f61908bd5dc..bec1d635311 100644
--- a/lib/upgrade.txt
+++ b/lib/upgrade.txt
@@ -2,7 +2,7 @@ This files describes API changes in core libraries and APIs,
 information provided here is intended especially for developers.
 === 4.1 ===
 
-* HTMLPurifier has been upgraded to the latest version - 4.14.0
+* HTMLPurifier has been upgraded to the latest version - 4.16.0
 * A process to deprecate capabilities by flagging them in the access.php by adding a $deprecatedcapabilities variable (an array).
   This array will list the deprecated capabilities and a possible replacement. Once we declare the capability as deprecated, a debugging
   message will be displayed (in DEBUG_DEVELOPPER mode only) when using the deprecated capability.