diff --git a/include/thirdparty/wp/kses.php b/include/thirdparty/wp/kses.php
index 2d6d796..0c5a04a 100644
--- a/include/thirdparty/wp/kses.php
+++ b/include/thirdparty/wp/kses.php
@@ -1,4 +1,5 @@
 <?php
+defined('is_running') or die('Not an entry point...');
 /**
  * kses 0.2.2 - HTML/XHTML filter that only allows some elements and attributes
  * Copyright (C) 2002, 2003, 2005  Ulf Harnhammar
@@ -28,424 +29,925 @@
  *
  * @package External
  * @subpackage KSES
- *
  */
 
+/**
+ * Specifies the default allowable HTML tags.
+ *
+ * Using `CUSTOM_TAGS` is not recommended and should be considered deprecated. The
+ * {@see 'wp_kses_allowed_html'} filter is more powerful and supplies context.
+ *
+ * @see wp_kses_allowed_html()
+ * @since 1.2.0
+ *
+ * @var array[]|false Array of default allowable HTML tags, or false to use the defaults.
+ */
+if ( ! defined( 'CUSTOM_TAGS' ) ) {
+	define( 'CUSTOM_TAGS', false );
+}
 
+// Ensure that these variables are added to the global namespace
+// (e.g. if using namespaces / autoload in the current PHP environment).
+global $allowedposttags, $allowedtags, $allowedentitynames, $allowedxmlentitynames;
 
+if ( ! CUSTOM_TAGS ) {
 	/**
-	 * Kses global for default allowable HTML tags.
+	 * KSES global for default allowable HTML tags.
 	 *
-	 * Can be override by using CUSTOM_TAGS constant.
+	 * Can be overridden with the `CUSTOM_TAGS` constant.
 	 *
-	 * @global array $allowedposttags
+	 * @var array[] $allowedposttags Array of default allowable HTML tags.
 	 * @since 2.0.0
 	 */
-	global $allowedposttags, $allowedentitynames, $allowedprotocols;
-
 	$allowedposttags = array(
-		'address' => array(),
-		'a' => array(
-			'href' => true,
-			'rel' => true,
-			'rev' => true,
-			'name' => true,
-			'target' => true,
+		'address'    => array(),
+		'a'          => array(
+			'href'     => true,
+			'rel'      => true,
+			'rev'      => true,
+			'name'     => true,
+			'target'   => true,
+			'download' => array(
+				'valueless' => 'y',
+			),
 		),
-		'abbr' => array(),
-		'acronym' => array(),
-		'area' => array(
-			'alt' => true,
+		'abbr'       => array(),
+		'acronym'    => array(),
+		'area'       => array(
+			'alt'    => true,
 			'coords' => true,
-			'href' => true,
+			'href'   => true,
 			'nohref' => true,
-			'shape' => true,
+			'shape'  => true,
 			'target' => true,
 		),
-		'article' => array(
-			'align' => true,
-			'dir' => true,
-			'lang' => true,
+		'article'    => array(
+			'align'    => true,
+			'dir'      => true,
+			'lang'     => true,
 			'xml:lang' => true,
 		),
-		'aside' => array(
-			'align' => true,
-			'dir' => true,
-			'lang' => true,
+		'aside'      => array(
+			'align'    => true,
+			'dir'      => true,
+			'lang'     => true,
 			'xml:lang' => true,
 		),
-		'b' => array(),
-		'big' => array(),
+		'audio'      => array(
+			'autoplay' => true,
+			'controls' => true,
+			'loop'     => true,
+			'muted'    => true,
+			'preload'  => true,
+			'src'      => true,
+		),
+		'b'          => array(),
+		'bdo'        => array(
+			'dir' => true,
+		),
+		'big'        => array(),
 		'blockquote' => array(
-			'cite' => true,
-			'lang' => true,
+			'cite'     => true,
+			'lang'     => true,
 			'xml:lang' => true,
 		),
-		'br' => array(),
-		'button' => array(
+		'br'         => array(),
+		'button'     => array(
 			'disabled' => true,
-			'name' => true,
-			'type' => true,
-			'value' => true,
+			'name'     => true,
+			'type'     => true,
+			'value'    => true,
 		),
-		'caption' => array(
+		'caption'    => array(
 			'align' => true,
 		),
-		'cite' => array(
-			'dir' => true,
+		'cite'       => array(
+			'dir'  => true,
 			'lang' => true,
 		),
-		'code' => array(),
-		'col' => array(
-			'align' => true,
-			'char' => true,
+		'code'       => array(),
+		'col'        => array(
+			'align'   => true,
+			'char'    => true,
 			'charoff' => true,
-			'span' => true,
-			'dir' => true,
-			'valign' => true,
-			'width' => true,
+			'span'    => true,
+			'dir'     => true,
+			'valign'  => true,
+			'width'   => true,
 		),
-		'del' => array(
+		'colgroup'   => array(
+			'align'   => true,
+			'char'    => true,
+			'charoff' => true,
+			'span'    => true,
+			'valign'  => true,
+			'width'   => true,
+		),
+		'del'        => array(
 			'datetime' => true,
 		),
-		'dd' => array(),
-		'details' => array(
-			'align' => true,
-			'dir' => true,
-			'lang' => true,
-			'open' => true,
+		'dd'         => array(),
+		'dfn'        => array(),
+		'details'    => array(
+			'align'    => true,
+			'dir'      => true,
+			'lang'     => true,
+			'open'     => true,
 			'xml:lang' => true,
 		),
-		'div' => array(
-			'align' => true,
-			'dir' => true,
-			'lang' => true,
+		'div'        => array(
+			'align'    => true,
+			'dir'      => true,
+			'lang'     => true,
 			'xml:lang' => true,
-			'style' => true,
 		),
-		'dl' => array(),
-		'dt' => array(),
-		'em' => array(),
-		'fieldset' => array(),
-		'figure' => array(
-			'align' => true,
-			'dir' => true,
-			'lang' => true,
+		'dl'         => array(),
+		'dt'         => array(),
+		'em'         => array(),
+		'fieldset'   => array(),
+		'figure'     => array(
+			'align'    => true,
+			'dir'      => true,
+			'lang'     => true,
 			'xml:lang' => true,
 		),
 		'figcaption' => array(
-			'align' => true,
-			'dir' => true,
-			'lang' => true,
+			'align'    => true,
+			'dir'      => true,
+			'lang'     => true,
 			'xml:lang' => true,
 		),
-		'font' => array(
+		'font'       => array(
 			'color' => true,
-			'face' => true,
-			'size' => true,
+			'face'  => true,
+			'size'  => true,
 		),
-		'footer' => array(
-			'align' => true,
-			'dir' => true,
-			'lang' => true,
+		'footer'     => array(
+			'align'    => true,
+			'dir'      => true,
+			'lang'     => true,
 			'xml:lang' => true,
 		),
-		'form' => array(
-			'action' => true,
-			'accept' => true,
-			'accept-charset' => true,
-			'enctype' => true,
-			'method' => true,
-			'name' => true,
-			'target' => true,
-		),
-		'h1' => array(
+		'h1'         => array(
 			'align' => true,
 		),
-		'h2' => array(
+		'h2'         => array(
 			'align' => true,
 		),
-		'h3' => array(
+		'h3'         => array(
 			'align' => true,
 		),
-		'h4' => array(
+		'h4'         => array(
 			'align' => true,
 		),
-		'h5' => array(
+		'h5'         => array(
 			'align' => true,
 		),
-		'h6' => array(
+		'h6'         => array(
 			'align' => true,
 		),
-		'header' => array(
-			'align' => true,
-			'dir' => true,
-			'lang' => true,
+		'header'     => array(
+			'align'    => true,
+			'dir'      => true,
+			'lang'     => true,
 			'xml:lang' => true,
 		),
-		'hgroup' => array(
-			'align' => true,
-			'dir' => true,
-			'lang' => true,
+		'hgroup'     => array(
+			'align'    => true,
+			'dir'      => true,
+			'lang'     => true,
 			'xml:lang' => true,
 		),
-		'hr' => array(
-			'align' => true,
+		'hr'         => array(
+			'align'   => true,
 			'noshade' => true,
-			'size' => true,
-			'width' => true,
+			'size'    => true,
+			'width'   => true,
 		),
-		'i' => array(),
-		'img' => array(
-			'alt' => true,
-			'align' => true,
-			'border' => true,
-			'height' => true,
-			'hspace' => true,
+		'i'          => array(),
+		'img'        => array(
+			'alt'      => true,
+			'align'    => true,
+			'border'   => true,
+			'height'   => true,
+			'hspace'   => true,
+			'loading'  => true,
 			'longdesc' => true,
-			'vspace' => true,
-			'src' => true,
-			'usemap' => true,
-			'width' => true,
+			'vspace'   => true,
+			'src'      => true,
+			'usemap'   => true,
+			'width'    => true,
 		),
-		'ins' => array(
+		'ins'        => array(
 			'datetime' => true,
-			'cite' => true,
+			'cite'     => true,
 		),
-		'kbd' => array(),
-		'label' => array(
+		'kbd'        => array(),
+		'label'      => array(
 			'for' => true,
 		),
-		'legend' => array(
+		'legend'     => array(
 			'align' => true,
 		),
-		'li' => array(
+		'li'         => array(
 			'align' => true,
+			'value' => true,
 		),
-		'map' => array(
+		'main'       => array(
+			'align'    => true,
+			'dir'      => true,
+			'lang'     => true,
+			'xml:lang' => true,
+		),
+		'map'        => array(
 			'name' => true,
 		),
-		'menu' => array(
+		'mark'       => array(),
+		'menu'       => array(
 			'type' => true,
 		),
-		'nav' => array(
-			'align' => true,
-			'dir' => true,
-			'lang' => true,
+		'nav'        => array(
+			'align'    => true,
+			'dir'      => true,
+			'lang'     => true,
 			'xml:lang' => true,
 		),
-		'p' => array(
-			'align' => true,
-			'dir' => true,
-			'lang' => true,
+		'p'          => array(
+			'align'    => true,
+			'dir'      => true,
+			'lang'     => true,
 			'xml:lang' => true,
 		),
-		'pre' => array(
+		'pre'        => array(
 			'width' => true,
 		),
-		'q' => array(
+		'q'          => array(
 			'cite' => true,
 		),
-		's' => array(),
-		'span' => array(
-			'dir' => true,
-			'align' => true,
-			'lang' => true,
+		's'          => array(),
+		'samp'       => array(),
+		'span'       => array(
+			'dir'      => true,
+			'align'    => true,
+			'lang'     => true,
 			'xml:lang' => true,
 		),
-		'section' => array(
-			'align' => true,
-			'dir' => true,
-			'lang' => true,
+		'section'    => array(
+			'align'    => true,
+			'dir'      => true,
+			'lang'     => true,
 			'xml:lang' => true,
 		),
-		'small' => array(),
-		'strike' => array(),
-		'strong' => array(),
-		'sub' => array(),
-		'summary' => array(
-			'align' => true,
-			'dir' => true,
-			'lang' => true,
+		'small'      => array(),
+		'strike'     => array(),
+		'strong'     => array(),
+		'sub'        => array(),
+		'summary'    => array(
+			'align'    => true,
+			'dir'      => true,
+			'lang'     => true,
 			'xml:lang' => true,
 		),
-		'sup' => array(),
-		'table' => array(
-			'align' => true,
-			'bgcolor' => true,
-			'border' => true,
+		'sup'        => array(),
+		'table'      => array(
+			'align'       => true,
+			'bgcolor'     => true,
+			'border'      => true,
 			'cellpadding' => true,
 			'cellspacing' => true,
-			'dir' => true,
-			'rules' => true,
-			'summary' => true,
-			'width' => true,
+			'dir'         => true,
+			'rules'       => true,
+			'summary'     => true,
+			'width'       => true,
 		),
-		'tbody' => array(
-			'align' => true,
-			'char' => true,
+		'tbody'      => array(
+			'align'   => true,
+			'char'    => true,
 			'charoff' => true,
-			'valign' => true,
+			'valign'  => true,
 		),
-		'td' => array(
-			'abbr' => true,
-			'align' => true,
-			'axis' => true,
+		'td'         => array(
+			'abbr'    => true,
+			'align'   => true,
+			'axis'    => true,
 			'bgcolor' => true,
-			'char' => true,
+			'char'    => true,
 			'charoff' => true,
 			'colspan' => true,
-			'dir' => true,
+			'dir'     => true,
 			'headers' => true,
-			'height' => true,
-			'nowrap' => true,
+			'height'  => true,
+			'nowrap'  => true,
 			'rowspan' => true,
-			'scope' => true,
-			'valign' => true,
-			'width' => true,
+			'scope'   => true,
+			'valign'  => true,
+			'width'   => true,
 		),
-		'textarea' => array(
-			'cols' => true,
-			'rows' => true,
+		'textarea'   => array(
+			'cols'     => true,
+			'rows'     => true,
 			'disabled' => true,
-			'name' => true,
+			'name'     => true,
 			'readonly' => true,
 		),
-		'tfoot' => array(
-			'align' => true,
-			'char' => true,
+		'tfoot'      => array(
+			'align'   => true,
+			'char'    => true,
 			'charoff' => true,
-			'valign' => true,
+			'valign'  => true,
 		),
-		'th' => array(
-			'abbr' => true,
-			'align' => true,
-			'axis' => true,
+		'th'         => array(
+			'abbr'    => true,
+			'align'   => true,
+			'axis'    => true,
 			'bgcolor' => true,
-			'char' => true,
+			'char'    => true,
 			'charoff' => true,
 			'colspan' => true,
 			'headers' => true,
-			'height' => true,
-			'nowrap' => true,
+			'height'  => true,
+			'nowrap'  => true,
 			'rowspan' => true,
-			'scope' => true,
-			'valign' => true,
-			'width' => true,
+			'scope'   => true,
+			'valign'  => true,
+			'width'   => true,
 		),
-		'thead' => array(
-			'align' => true,
-			'char' => true,
+		'thead'      => array(
+			'align'   => true,
+			'char'    => true,
 			'charoff' => true,
-			'valign' => true,
+			'valign'  => true,
 		),
-		'title' => array(),
-		'tr' => array(
-			'align' => true,
+		'title'      => array(),
+		'tr'         => array(
+			'align'   => true,
 			'bgcolor' => true,
-			'char' => true,
+			'char'    => true,
 			'charoff' => true,
-			'valign' => true,
+			'valign'  => true,
 		),
-		'tt' => array(),
-		'u' => array(),
-		'ul' => array(
+		'track'      => array(
+			'default' => true,
+			'kind'    => true,
+			'label'   => true,
+			'src'     => true,
+			'srclang' => true,
+		),
+		'tt'         => array(),
+		'u'          => array(),
+		'ul'         => array(
 			'type' => true,
 		),
-		'ol' => array(
-			'start' => true,
-			'type' => true,
+		'ol'         => array(
+			'start'    => true,
+			'type'     => true,
+			'reversed' => true,
+		),
+		'var'        => array(),
+		'video'      => array(
+			'autoplay'    => true,
+			'controls'    => true,
+			'height'      => true,
+			'loop'        => true,
+			'muted'       => true,
+			'playsinline' => true,
+			'poster'      => true,
+			'preload'     => true,
+			'src'         => true,
+			'width'       => true,
 		),
-		'var' => array(),
 	);
 
+	/**
+	 * @var array[] $allowedtags Array of KSES allowed HTML elements.
+	 * @since 1.0.0
+	 */
+	$allowedtags = array(
+		'a'          => array(
+			'href'  => true,
+			'title' => true,
+		),
+		'abbr'       => array(
+			'title' => true,
+		),
+		'acronym'    => array(
+			'title' => true,
+		),
+		'b'          => array(),
+		'blockquote' => array(
+			'cite' => true,
+		),
+		'cite'       => array(),
+		'code'       => array(),
+		'del'        => array(
+			'datetime' => true,
+		),
+		'em'         => array(),
+		'i'          => array(),
+		'q'          => array(
+			'cite' => true,
+		),
+		's'          => array(),
+		'strike'     => array(),
+		'strong'     => array(),
+	);
+
+	/**
+	 * @var string[] $allowedentitynames Array of KSES allowed HTML entitity names.
+	 * @since 1.0.0
+	 */
 	$allowedentitynames = array(
-		'nbsp',    'iexcl',  'cent',    'pound',  'curren', 'yen',
-		'brvbar',  'sect',   'uml',     'copy',   'ordf',   'laquo',
-		'not',     'shy',    'reg',     'macr',   'deg',    'plusmn',
-		'acute',   'micro',  'para',    'middot', 'cedil',  'ordm',
-		'raquo',   'iquest', 'Agrave',  'Aacute', 'Acirc',  'Atilde',
-		'Auml',    'Aring',  'AElig',   'Ccedil', 'Egrave', 'Eacute',
-		'Ecirc',   'Euml',   'Igrave',  'Iacute', 'Icirc',  'Iuml',
-		'ETH',     'Ntilde', 'Ograve',  'Oacute', 'Ocirc',  'Otilde',
-		'Ouml',    'times',  'Oslash',  'Ugrave', 'Uacute', 'Ucirc',
-		'Uuml',    'Yacute', 'THORN',   'szlig',  'agrave', 'aacute',
-		'acirc',   'atilde', 'auml',    'aring',  'aelig',  'ccedil',
-		'egrave',  'eacute', 'ecirc',   'euml',   'igrave', 'iacute',
-		'icirc',   'iuml',   'eth',     'ntilde', 'ograve', 'oacute',
-		'ocirc',   'otilde', 'ouml',    'divide', 'oslash', 'ugrave',
-		'uacute',  'ucirc',  'uuml',    'yacute', 'thorn',  'yuml',
-		'quot',    'amp',    'lt',      'gt',     'apos',   'OElig',
-		'oelig',   'Scaron', 'scaron',  'Yuml',   'circ',   'tilde',
-		'ensp',    'emsp',   'thinsp',  'zwnj',   'zwj',    'lrm',
-		'rlm',     'ndash',  'mdash',   'lsquo',  'rsquo',  'sbquo',
-		'ldquo',   'rdquo',  'bdquo',   'dagger', 'Dagger', 'permil',
-		'lsaquo',  'rsaquo', 'euro',    'fnof',   'Alpha',  'Beta',
-		'Gamma',   'Delta',  'Epsilon', 'Zeta',   'Eta',    'Theta',
-		'Iota',    'Kappa',  'Lambda',  'Mu',     'Nu',     'Xi',
-		'Omicron', 'Pi',     'Rho',     'Sigma',  'Tau',    'Upsilon',
-		'Phi',     'Chi',    'Psi',     'Omega',  'alpha',  'beta',
-		'gamma',   'delta',  'epsilon', 'zeta',   'eta',    'theta',
-		'iota',    'kappa',  'lambda',  'mu',     'nu',     'xi',
-		'omicron', 'pi',     'rho',     'sigmaf', 'sigma',  'tau',
-		'upsilon', 'phi',    'chi',     'psi',    'omega',  'thetasym',
-		'upsih',   'piv',    'bull',    'hellip', 'prime',  'Prime',
-		'oline',   'frasl',  'weierp',  'image',  'real',   'trade',
-		'alefsym', 'larr',   'uarr',    'rarr',   'darr',   'harr',
-		'crarr',   'lArr',   'uArr',    'rArr',   'dArr',   'hArr',
-		'forall',  'part',   'exist',   'empty',  'nabla',  'isin',
-		'notin',   'ni',     'prod',    'sum',    'minus',  'lowast',
-		'radic',   'prop',   'infin',   'ang',    'and',    'or',
-		'cap',     'cup',    'int',     'sim',    'cong',   'asymp',
-		'ne',      'equiv',  'le',      'ge',     'sub',    'sup',
-		'nsub',    'sube',   'supe',    'oplus',  'otimes', 'perp',
-		'sdot',    'lceil',  'rceil',   'lfloor', 'rfloor', 'lang',
-		'rang',    'loz',    'spades',  'clubs',  'hearts', 'diams',
+		'nbsp',
+		'iexcl',
+		'cent',
+		'pound',
+		'curren',
+		'yen',
+		'brvbar',
+		'sect',
+		'uml',
+		'copy',
+		'ordf',
+		'laquo',
+		'not',
+		'shy',
+		'reg',
+		'macr',
+		'deg',
+		'plusmn',
+		'acute',
+		'micro',
+		'para',
+		'middot',
+		'cedil',
+		'ordm',
+		'raquo',
+		'iquest',
+		'Agrave',
+		'Aacute',
+		'Acirc',
+		'Atilde',
+		'Auml',
+		'Aring',
+		'AElig',
+		'Ccedil',
+		'Egrave',
+		'Eacute',
+		'Ecirc',
+		'Euml',
+		'Igrave',
+		'Iacute',
+		'Icirc',
+		'Iuml',
+		'ETH',
+		'Ntilde',
+		'Ograve',
+		'Oacute',
+		'Ocirc',
+		'Otilde',
+		'Ouml',
+		'times',
+		'Oslash',
+		'Ugrave',
+		'Uacute',
+		'Ucirc',
+		'Uuml',
+		'Yacute',
+		'THORN',
+		'szlig',
+		'agrave',
+		'aacute',
+		'acirc',
+		'atilde',
+		'auml',
+		'aring',
+		'aelig',
+		'ccedil',
+		'egrave',
+		'eacute',
+		'ecirc',
+		'euml',
+		'igrave',
+		'iacute',
+		'icirc',
+		'iuml',
+		'eth',
+		'ntilde',
+		'ograve',
+		'oacute',
+		'ocirc',
+		'otilde',
+		'ouml',
+		'divide',
+		'oslash',
+		'ugrave',
+		'uacute',
+		'ucirc',
+		'uuml',
+		'yacute',
+		'thorn',
+		'yuml',
+		'quot',
+		'amp',
+		'lt',
+		'gt',
+		'apos',
+		'OElig',
+		'oelig',
+		'Scaron',
+		'scaron',
+		'Yuml',
+		'circ',
+		'tilde',
+		'ensp',
+		'emsp',
+		'thinsp',
+		'zwnj',
+		'zwj',
+		'lrm',
+		'rlm',
+		'ndash',
+		'mdash',
+		'lsquo',
+		'rsquo',
+		'sbquo',
+		'ldquo',
+		'rdquo',
+		'bdquo',
+		'dagger',
+		'Dagger',
+		'permil',
+		'lsaquo',
+		'rsaquo',
+		'euro',
+		'fnof',
+		'Alpha',
+		'Beta',
+		'Gamma',
+		'Delta',
+		'Epsilon',
+		'Zeta',
+		'Eta',
+		'Theta',
+		'Iota',
+		'Kappa',
+		'Lambda',
+		'Mu',
+		'Nu',
+		'Xi',
+		'Omicron',
+		'Pi',
+		'Rho',
+		'Sigma',
+		'Tau',
+		'Upsilon',
+		'Phi',
+		'Chi',
+		'Psi',
+		'Omega',
+		'alpha',
+		'beta',
+		'gamma',
+		'delta',
+		'epsilon',
+		'zeta',
+		'eta',
+		'theta',
+		'iota',
+		'kappa',
+		'lambda',
+		'mu',
+		'nu',
+		'xi',
+		'omicron',
+		'pi',
+		'rho',
+		'sigmaf',
+		'sigma',
+		'tau',
+		'upsilon',
+		'phi',
+		'chi',
+		'psi',
+		'omega',
+		'thetasym',
+		'upsih',
+		'piv',
+		'bull',
+		'hellip',
+		'prime',
+		'Prime',
+		'oline',
+		'frasl',
+		'weierp',
+		'image',
+		'real',
+		'trade',
+		'alefsym',
+		'larr',
+		'uarr',
+		'rarr',
+		'darr',
+		'harr',
+		'crarr',
+		'lArr',
+		'uArr',
+		'rArr',
+		'dArr',
+		'hArr',
+		'forall',
+		'part',
+		'exist',
+		'empty',
+		'nabla',
+		'isin',
+		'notin',
+		'ni',
+		'prod',
+		'sum',
+		'minus',
+		'lowast',
+		'radic',
+		'prop',
+		'infin',
+		'ang',
+		'and',
+		'or',
+		'cap',
+		'cup',
+		'int',
+		'sim',
+		'cong',
+		'asymp',
+		'ne',
+		'equiv',
+		'le',
+		'ge',
+		'sub',
+		'sup',
+		'nsub',
+		'sube',
+		'supe',
+		'oplus',
+		'otimes',
+		'perp',
+		'sdot',
+		'lceil',
+		'rceil',
+		'lfloor',
+		'rfloor',
+		'lang',
+		'rang',
+		'loz',
+		'spades',
+		'clubs',
+		'hearts',
+		'diams',
+		'sup1',
+		'sup2',
+		'sup3',
+		'frac14',
+		'frac12',
+		'frac34',
+		'there4',
 	);
 
-	$allowedprotocols = array( 'http', 'https', 'ftp', 'ftps', 'mailto', 'news', 'irc', 'gopher', 'nntp', 'feed', 'telnet', 'mms', 'rtsp', 'svn' );
-
+	/**
+	 * @var string[] $allowedxmlentitynames Array of KSES allowed XML entitity names.
+	 * @since 5.5.0
+	 */
+	$allowedxmlnamedentities = array(
+		'amp',
+		'lt',
+		'gt',
+		'apos',
+		'quot',
+	);
 
 	$allowedposttags = array_map( '_wp_add_global_attributes', $allowedposttags );
-
-
-/**
- * Filters content and keeps only allowable HTML elements.
- *
- * This function makes sure that only the allowed HTML element names, attribute
- * names and attribute values plus only sane HTML entities will occur in
- * $string. You have to remove any slashes from PHP's magic quotes before you
- * call this function.
- *
- * The default allowed protocols are 'http', 'https', 'ftp', 'mailto', 'news',
- * 'irc', 'gopher', 'nntp', 'feed', 'telnet, 'mms', 'rtsp' and 'svn'. This
- * covers all common link protocols, except for 'javascript' which should not
- * be allowed for untrusted users.
- *
- * @since 1.0.0
- *
- * @param string $string Content to filter through kses
- * @param array $allowed_html List of allowed HTML elements
- * @param array $allowed_protocols Optional. Allowed protocol in links.
- * @return string Filtered content with only allowed HTML elements
- */
-function wp_kses( $string, $allowed_html, $allowed_protocols = array() ) {
-	global $allowedprotocols;
-	if ( empty( $allowed_protocols ) )
-		$allowed_protocols = $allowedprotocols;
-	$string = wp_kses_no_null($string);
-	$string = wp_kses_js_entities($string);
-	$string = wp_kses_normalize_entities($string);
-	return wp_kses_split($string, $allowed_html, $allowed_protocols);
+} else {
+	$allowedtags     = wp_kses_array_lc( $allowedtags );
+	$allowedposttags = wp_kses_array_lc( $allowedposttags );
 }
 
-
 /**
- * This function returns kses' version number.
+ * Filters text content and strips out disallowed HTML.
+ *
+ * This function makes sure that only the allowed HTML element names, attribute
+ * names, attribute values, and HTML entities will occur in the given text string.
+ *
+ * This function expects unslashed data.
+ *
+ * @see wp_kses_post() for specifically filtering post content and fields.
+ * @see wp_allowed_protocols() for the default allowed protocols in link URLs.
  *
  * @since 1.0.0
  *
- * @return string KSES Version Number
+ * @param string         $string            Text content to filter.
+ * @param array[]|string $allowed_html      An array of allowed HTML elements and attributes,
+ *                                          or a context name such as 'post'. See wp_kses_allowed_html()
+ *                                          for the list of accepted context names.
+ * @param string[]       $allowed_protocols Array of allowed URL protocols.
+ * @return string Filtered content containing only the allowed HTML.
+ */
+function wp_kses( $string, $allowed_html, $allowed_protocols = array() ) {
+	if ( empty( $allowed_protocols ) ) {
+		$allowed_protocols = wp_allowed_protocols();
+	}
+
+	$string = wp_kses_no_null( $string, array( 'slash_zero' => 'keep' ) );
+	$string = wp_kses_normalize_entities( $string );
+	$string = wp_kses_hook( $string, $allowed_html, $allowed_protocols );
+
+	return wp_kses_split( $string, $allowed_html, $allowed_protocols );
+}
+
+/**
+ * Filters one HTML attribute and ensures its value is allowed.
+ *
+ * This function can escape data in some situations where `wp_kses()` must strip the whole attribute.
+ *
+ * @since 4.2.3
+ *
+ * @param string $string  The 'whole' attribute, including name and value.
+ * @param string $element The HTML element name to which the attribute belongs.
+ * @return string Filtered attribute.
+ */
+function wp_kses_one_attr( $string, $element ) {
+	$uris              = wp_kses_uri_attributes();
+	$allowed_html      = wp_kses_allowed_html( 'post' );
+	$allowed_protocols = wp_allowed_protocols();
+	$string            = wp_kses_no_null( $string, array( 'slash_zero' => 'keep' ) );
+
+	// Preserve leading and trailing whitespace.
+	$matches = array();
+	preg_match( '/^\s*/', $string, $matches );
+	$lead = $matches[0];
+	preg_match( '/\s*$/', $string, $matches );
+	$trail = $matches[0];
+	if ( empty( $trail ) ) {
+		$string = substr( $string, strlen( $lead ) );
+	} else {
+		$string = substr( $string, strlen( $lead ), -strlen( $trail ) );
+	}
+
+	// Parse attribute name and value from input.
+	$split = preg_split( '/\s*=\s*/', $string, 2 );
+	$name  = $split[0];
+	if ( count( $split ) == 2 ) {
+		$value = $split[1];
+
+		// Remove quotes surrounding $value.
+		// Also guarantee correct quoting in $string for this one attribute.
+		if ( '' === $value ) {
+			$quote = '';
+		} else {
+			$quote = $value[0];
+		}
+		if ( '"' === $quote || "'" === $quote ) {
+			if ( substr( $value, -1 ) != $quote ) {
+				return '';
+			}
+			$value = substr( $value, 1, -1 );
+		} else {
+			$quote = '"';
+		}
+
+		// Sanitize quotes, angle braces, and entities.
+		$value = esc_attr( $value );
+
+		// Sanitize URI values.
+		if ( in_array( strtolower( $name ), $uris, true ) ) {
+			$value = wp_kses_bad_protocol( $value, $allowed_protocols );
+		}
+
+		$string = "$name=$quote$value$quote";
+		$vless  = 'n';
+	} else {
+		$value = '';
+		$vless = 'y';
+	}
+
+	// Sanitize attribute by name.
+	wp_kses_attr_check( $name, $value, $string, $vless, $element, $allowed_html );
+
+	// Restore whitespace.
+	return $lead . $string . $trail;
+}
+
+/**
+ * Returns an array of allowed HTML tags and attributes for a given context.
+ *
+ * @since 3.5.0
+ * @since 5.0.1 `form` removed as allowable HTML tag.
+ *
+ * @global array $allowedposttags
+ * @global array $allowedtags
+ * @global array $allowedentitynames
+ *
+ * @param string|array $context The context for which to retrieve tags. Allowed values are 'post',
+ *                              'strip', 'data', 'entities', or the name of a field filter such as
+ *                              'pre_user_description'.
+ * @return array Array of allowed HTML tags and their allowed attributes.
+ */
+function wp_kses_allowed_html( $context = '' ) {
+	global $allowedposttags, $allowedtags, $allowedentitynames;
+
+	if ( is_array( $context ) ) {
+		/**
+		 * Filters the HTML that is allowed for a given context.
+		 *
+		 * @since 3.5.0
+		 *
+		 * @param array[]|string $context      Context to judge allowed tags by.
+		 * @param string         $context_type Context name.
+		 */
+		return apply_filters( 'wp_kses_allowed_html', $context, 'explicit' );
+	}
+
+	switch ( $context ) {
+		case 'post':
+			/** This filter is documented in wp-includes/kses.php */
+			$tags = apply_filters( 'wp_kses_allowed_html', $allowedposttags, $context );
+
+			// 5.0.1 removed the `<form>` tag, allow it if a filter is allowing it's sub-elements `<input>` or `<select>`.
+			if ( ! CUSTOM_TAGS && ! isset( $tags['form'] ) && ( isset( $tags['input'] ) || isset( $tags['select'] ) ) ) {
+				$tags = $allowedposttags;
+
+				$tags['form'] = array(
+					'action'         => true,
+					'accept'         => true,
+					'accept-charset' => true,
+					'enctype'        => true,
+					'method'         => true,
+					'name'           => true,
+					'target'         => true,
+				);
+
+				/** This filter is documented in wp-includes/kses.php */
+				$tags = apply_filters( 'wp_kses_allowed_html', $tags, $context );
+			}
+
+			return $tags;
+
+		case 'user_description':
+		case 'pre_user_description':
+			$tags             = $allowedtags;
+			$tags['a']['rel'] = true;
+			/** This filter is documented in wp-includes/kses.php */
+			return apply_filters( 'wp_kses_allowed_html', $tags, $context );
+
+		case 'strip':
+			/** This filter is documented in wp-includes/kses.php */
+			return apply_filters( 'wp_kses_allowed_html', array(), $context );
+
+		case 'entities':
+			/** This filter is documented in wp-includes/kses.php */
+			return apply_filters( 'wp_kses_allowed_html', $allowedentitynames, $context );
+
+		case 'data':
+		default:
+			/** This filter is documented in wp-includes/kses.php */
+			return apply_filters( 'wp_kses_allowed_html', $allowedtags, $context );
+	}
+}
+
+/**
+ * You add any KSES hooks here.
+ *
+ * There is currently only one KSES WordPress hook, {@see 'pre_kses'}, and it is called here.
+ * All parameters are passed to the hooks and expected to receive a string.
+ *
+ * @since 1.0.0
+ *
+ * @param string         $string            Content to filter through KSES.
+ * @param array[]|string $allowed_html      An array of allowed HTML elements and attributes,
+ *                                          or a context name such as 'post'. See wp_kses_allowed_html()
+ *                                          for the list of accepted context names.
+ * @param string[]       $allowed_protocols Array of allowed URL protocols.
+ * @return string Filtered content through {@see 'pre_kses'} hook.
+ */
+function wp_kses_hook( $string, $allowed_html, $allowed_protocols ) {
+	/**
+	 * Filters content to be run through KSES.
+	 *
+	 * @since 2.3.0
+	 *
+	 * @param string         $string            Content to filter through KSES.
+	 * @param array[]|string $allowed_html      An array of allowed HTML elements and attributes,
+	 *                                          or a context name such as 'post'. See wp_kses_allowed_html()
+	 *                                          for the list of accepted context names.
+	 * @param string[]       $allowed_protocols Array of allowed URL protocols.
+	 */
+	return apply_filters( 'pre_kses', $string, $allowed_html, $allowed_protocols );
+}
+
+/**
+ * Returns the version number of KSES.
+ *
+ * @since 1.0.0
+ *
+ * @return string KSES version number.
  */
 function wp_kses_version() {
 	return '0.2.2';
@@ -454,39 +956,106 @@ function wp_kses_version() {
 /**
  * Searches for HTML tags, no matter how malformed.
  *
- * It also matches stray ">" characters.
+ * It also matches stray `>` characters.
  *
  * @since 1.0.0
  *
- * @param string $string Content to filter
- * @param array $allowed_html Allowed HTML elements
- * @param array $allowed_protocols Allowed protocols to keep
+ * @global array[]|string $pass_allowed_html      An array of allowed HTML elements and attributes,
+ *                                                or a context name such as 'post'.
+ * @global string[]       $pass_allowed_protocols Array of allowed URL protocols.
+ *
+ * @param string         $string            Content to filter.
+ * @param array[]|string $allowed_html      An array of allowed HTML elements and attributes,
+ *                                          or a context name such as 'post'. See wp_kses_allowed_html()
+ *                                          for the list of accepted context names.
+ * @param string[]       $allowed_protocols Array of allowed URL protocols.
  * @return string Content with fixed HTML tags
  */
 function wp_kses_split( $string, $allowed_html, $allowed_protocols ) {
 	global $pass_allowed_html, $pass_allowed_protocols;
-	$pass_allowed_html = $allowed_html;
+
+	$pass_allowed_html      = $allowed_html;
 	$pass_allowed_protocols = $allowed_protocols;
+
 	return preg_replace_callback( '%(<!--.*?(-->|$))|(<[^>]*(>|$)|>)%', '_wp_kses_split_callback', $string );
 }
 
 /**
- * Callback for wp_kses_split.
+ * Returns an array of HTML attribute names whose value contains a URL.
+ *
+ * This function returns a list of all HTML attributes that must contain
+ * a URL according to the HTML specification.
+ *
+ * This list includes URI attributes both allowed and disallowed by KSES.
+ *
+ * @link https://developer.mozilla.org/en-US/docs/Web/HTML/Attributes
+ *
+ * @since 5.0.1
+ *
+ * @return string[] HTML attribute names whose value contains a URL.
+ */
+function wp_kses_uri_attributes() {
+	$uri_attributes = array(
+		'action',
+		'archive',
+		'background',
+		'cite',
+		'classid',
+		'codebase',
+		'data',
+		'formaction',
+		'href',
+		'icon',
+		'longdesc',
+		'manifest',
+		'poster',
+		'profile',
+		'src',
+		'usemap',
+		'xmlns',
+	);
+
+	/**
+	 * Filters the list of attributes that are required to contain a URL.
+	 *
+	 * Use this filter to add any `data-` attributes that are required to be
+	 * validated as a URL.
+	 *
+	 * @since 5.0.1
+	 *
+	 * @param string[] $uri_attributes HTML attribute names whose value contains a URL.
+	 */
+	$uri_attributes = apply_filters( 'wp_kses_uri_attributes', $uri_attributes );
+
+	return $uri_attributes;
+}
+
+/**
+ * Callback for `wp_kses_split()`.
  *
  * @since 3.1.0
  * @access private
+ * @ignore
+ *
+ * @global array[]|string $pass_allowed_html      An array of allowed HTML elements and attributes,
+ *                                                or a context name such as 'post'.
+ * @global string[]       $pass_allowed_protocols Array of allowed URL protocols.
+ *
+ * @param array $matches preg_replace regexp matches
+ * @return string
  */
 function _wp_kses_split_callback( $match ) {
 	global $pass_allowed_html, $pass_allowed_protocols;
+
 	return wp_kses_split2( $match[0], $pass_allowed_html, $pass_allowed_protocols );
 }
 
 /**
- * Callback for wp_kses_split for fixing malformed HTML tags.
+ * Callback for `wp_kses_split()` for fixing malformed HTML tags.
  *
  * This function does a lot of work. It rejects some very malformed things like
- * <:::>. It returns an empty string, if the element isn't allowed (look ma, no
- * strip_tags()!). Otherwise it splits the tag into an element and an attribute
+ * `<:::>`. It returns an empty string, if the element isn't allowed (look ma, no
+ * `strip_tags()`!). Otherwise it splits the tag into an element and an attribute
  * list.
  *
  * After the tag is split into an element and an attribute list, it is run
@@ -494,50 +1063,62 @@ function _wp_kses_split_callback( $match ) {
  * completed, will be returned.
  *
  * @access private
+ * @ignore
  * @since 1.0.0
- * @uses wp_kses_attr()
  *
- * @param string $string Content to filter
- * @param array $allowed_html Allowed HTML elements
- * @param array $allowed_protocols Allowed protocols to keep
+ * @param string         $string            Content to filter.
+ * @param array[]|string $allowed_html      An array of allowed HTML elements and attributes,
+ *                                          or a context name such as 'post'. See wp_kses_allowed_html()
+ *                                          for the list of accepted context names.
+ * @param string[]       $allowed_protocols Array of allowed URL protocols.
  * @return string Fixed HTML element
  */
-function wp_kses_split2($string, $allowed_html, $allowed_protocols) {
-	$string = wp_kses_stripslashes($string);
+function wp_kses_split2( $string, $allowed_html, $allowed_protocols ) {
+	$string = wp_kses_stripslashes( $string );
 
-	if (substr($string, 0, 1) != '<')
+	// It matched a ">" character.
+	if ( '<' !== substr( $string, 0, 1 ) ) {
 		return '&gt;';
-	# It matched a ">" character
+	}
 
-	if ( '<!--' == substr( $string, 0, 4 ) ) {
-		$string = str_replace( array('<!--', '-->'), '', $string );
-		while ( $string != ($newstring = wp_kses($string, $allowed_html, $allowed_protocols)) )
+	// Allow HTML comments.
+	if ( '<!--' === substr( $string, 0, 4 ) ) {
+		$string = str_replace( array( '<!--', '-->' ), '', $string );
+		while ( ( $newstring = wp_kses( $string, $allowed_html, $allowed_protocols ) ) != $string ) {
 			$string = $newstring;
-		if ( $string == '' )
+		}
+		if ( '' === $string ) {
 			return '';
-		// prevent multiple dashes in comments
-		$string = preg_replace('/--+/', '-', $string);
-		// prevent three dashes closing a comment
-		$string = preg_replace('/-$/', '', $string);
+		}
+		// Prevent multiple dashes in comments.
+		$string = preg_replace( '/--+/', '-', $string );
+		// Prevent three dashes closing a comment.
+		$string = preg_replace( '/-$/', '', $string );
 		return "<!--{$string}-->";
 	}
-	# Allow HTML comments
 
-	if (!preg_match('%^<\s*(/\s*)?([a-zA-Z0-9]+)([^>]*)>?$%', $string, $matches))
+	// It's seriously malformed.
+	if ( ! preg_match( '%^<\s*(/\s*)?([a-zA-Z0-9-]+)([^>]*)>?$%', $string, $matches ) ) {
 		return '';
-	# It's seriously malformed
+	}
 
-	$slash = trim($matches[1]);
-	$elem = $matches[2];
+	$slash    = trim( $matches[1] );
+	$elem     = $matches[2];
 	$attrlist = $matches[3];
 
-	if ( ! isset($allowed_html[strtolower($elem)]) )
-		return '';
-	# They are using a not allowed HTML element
+	if ( ! is_array( $allowed_html ) ) {
+		$allowed_html = wp_kses_allowed_html( $allowed_html );
+	}
 
-	if ($slash != '')
+	// They are using a not allowed HTML element.
+	if ( ! isset( $allowed_html[ strtolower( $elem ) ] ) ) {
+		return '';
+	}
+
+	// No attributes are allowed for closing elements.
+	if ( '' !== $slash ) {
 		return "</$elem>";
-	# No attributes are allowed for closing elements
+	}
 
 	return wp_kses_attr( $elem, $attrlist, $allowed_html, $allowed_protocols );
 }
@@ -545,84 +1126,138 @@ function wp_kses_split2($string, $allowed_html, $allowed_protocols) {
 /**
  * Removes all attributes, if none are allowed for this element.
  *
- * If some are allowed it calls wp_kses_hair() to split them further, and then
- * it builds up new HTML code from the data that kses_hair() returns. It also
- * removes "<" and ">" characters, if there are any left. One more thing it does
+ * If some are allowed it calls `wp_kses_hair()` to split them further, and then
+ * it builds up new HTML code from the data that `kses_hair()` returns. It also
+ * removes `<` and `>` characters, if there are any left. One more thing it does
  * is to check if the tag has a closing XHTML slash, and if it does, it puts one
  * in the returned code as well.
  *
  * @since 1.0.0
  *
- * @param string $element HTML element/tag
- * @param string $attr HTML attributes from HTML element to closing HTML element tag
- * @param array $allowed_html Allowed HTML elements
- * @param array $allowed_protocols Allowed protocols to keep
- * @return string Sanitized HTML element
+ * @param string         $element           HTML element/tag.
+ * @param string         $attr              HTML attributes from HTML element to closing HTML element tag.
+ * @param array[]|string $allowed_html      An array of allowed HTML elements and attributes,
+ *                                          or a context name such as 'post'. See wp_kses_allowed_html()
+ *                                          for the list of accepted context names.
+ * @param string[]       $allowed_protocols Array of allowed URL protocols.
+ * @return string Sanitized HTML element.
  */
-function wp_kses_attr($element, $attr, $allowed_html, $allowed_protocols) {
-	# Is there a closing XHTML slash at the end of the attributes?
-
+function wp_kses_attr( $element, $attr, $allowed_html, $allowed_protocols ) {
+	if ( ! is_array( $allowed_html ) ) {
+		$allowed_html = wp_kses_allowed_html( $allowed_html );
+	}
 
+	// Is there a closing XHTML slash at the end of the attributes?
 	$xhtml_slash = '';
-	if (preg_match('%\s*/\s*$%', $attr))
+	if ( preg_match( '%\s*/\s*$%', $attr ) ) {
 		$xhtml_slash = ' /';
+	}
 
-	# Are any attributes allowed at all for this element?
-	if ( ! isset($allowed_html[strtolower($element)]) || count($allowed_html[strtolower($element)]) == 0 )
+	// Are any attributes allowed at all for this element?
+	$element_low = strtolower( $element );
+	if ( empty( $allowed_html[ $element_low ] ) || true === $allowed_html[ $element_low ] ) {
 		return "<$element$xhtml_slash>";
+	}
 
-	# Split it
-	$attrarr = wp_kses_hair($attr, $allowed_protocols);
+	// Split it.
+	$attrarr = wp_kses_hair( $attr, $allowed_protocols );
 
-	# Go through $attrarr, and save the allowed attributes for this element
-	# in $attr2
+	// Go through $attrarr, and save the allowed attributes for this element
+	// in $attr2.
 	$attr2 = '';
-
-	$allowed_attr = $allowed_html[strtolower($element)];
-	foreach ($attrarr as $arreach) {
-		if ( ! isset( $allowed_attr[strtolower($arreach['name'])] ) )
-			continue; # the attribute is not allowed
-
-		$current = $allowed_attr[strtolower($arreach['name'])];
-		if ( $current == '' )
-			continue; # the attribute is not allowed
-
-		if ( strtolower( $arreach['name'] ) == 'style' ) {
-			$orig_value = $arreach['value'];
-			$value = safecss_filter_attr( $orig_value );
-
-			if ( empty( $value ) )
-				continue;
-
-			$arreach['value'] = $value;
-			$arreach['whole'] = str_replace( $orig_value, $value, $arreach['whole'] );
+	foreach ( $attrarr as $arreach ) {
+		if ( wp_kses_attr_check( $arreach['name'], $arreach['value'], $arreach['whole'], $arreach['vless'], $element, $allowed_html ) ) {
+			$attr2 .= ' ' . $arreach['whole'];
 		}
+	}
 
-		if ( ! is_array($current) ) {
-			$attr2 .= ' '.$arreach['whole'];
-		# there are no checks
-
-		} else {
-			# there are some checks
-			$ok = true;
-			foreach ($current as $currkey => $currval) {
-				if ( ! wp_kses_check_attr_val($arreach['value'], $arreach['vless'], $currkey, $currval) ) {
-					$ok = false;
-					break;
-				}
-			}
-
-			if ( $ok )
-				$attr2 .= ' '.$arreach['whole']; # it passed them
-		} # if !is_array($current)
-	} # foreach
-
-	# Remove any "<" or ">" characters
-	$attr2 = preg_replace('/[<>]/', '', $attr2);
+	// Remove any "<" or ">" characters.
+	$attr2 = preg_replace( '/[<>]/', '', $attr2 );
 
 	return "<$element$attr2$xhtml_slash>";
 }
 
+/**
+ * Determines whether an attribute is allowed.
+ *
+ * @since 4.2.3
+ * @since 5.0.0 Add support for `data-*` wildcard attributes.
+ *
+ * @param string $name         The attribute name. Passed by reference. Returns empty string when not allowed.
+ * @param string $value        The attribute value. Passed by reference. Returns a filtered value.
+ * @param string $whole        The `name=value` input. Passed by reference. Returns filtered input.
+ * @param string $vless        Whether the attribute is valueless. Use 'y' or 'n'.
+ * @param string $element      The name of the element to which this attribute belongs.
+ * @param array  $allowed_html The full list of allowed elements and attributes.
+ * @return bool Whether or not the attribute is allowed.
+ */
+function wp_kses_attr_check( &$name, &$value, &$whole, $vless, $element, $allowed_html ) {
+	$name_low    = strtolower( $name );
+	$element_low = strtolower( $element );
+
+	if ( ! isset( $allowed_html[ $element_low ] ) ) {
+		$name  = '';
+		$value = '';
+		$whole = '';
+		return false;
+	}
+
+	$allowed_attr = $allowed_html[ $element_low ];
+
+	if ( ! isset( $allowed_attr[ $name_low ] ) || '' === $allowed_attr[ $name_low ] ) {
+		/*
+		 * Allow `data-*` attributes.
+		 *
+		 * When specifying `$allowed_html`, the attribute name should be set as
+		 * `data-*` (not to be mixed with the HTML 4.0 `data` attribute, see
+		 * https://www.w3.org/TR/html40/struct/objects.html#adef-data).
+		 *
+		 * Note: the attribute name should only contain `A-Za-z0-9_-` chars,
+		 * double hyphens `--` are not accepted by WordPress.
+		 */
+		if ( strpos( $name_low, 'data-' ) === 0 && ! empty( $allowed_attr['data-*'] ) && preg_match( '/^data(?:-[a-z0-9_]+)+$/', $name_low, $match ) ) {
+			/*
+			 * Add the whole attribute name to the allowed attributes and set any restrictions
+			 * for the `data-*` attribute values for the current element.
+			 */
+			$allowed_attr[ $match[0] ] = $allowed_attr['data-*'];
+		} else {
+			$name  = '';
+			$value = '';
+			$whole = '';
+			return false;
+		}
+	}
+
+	if ( 'style' === $name_low ) {
+		$new_value = safecss_filter_attr( $value );
+
+		if ( empty( $new_value ) ) {
+			$name  = '';
+			$value = '';
+			$whole = '';
+			return false;
+		}
+
+		$whole = str_replace( $value, $new_value, $whole );
+		$value = $new_value;
+	}
+
+	if ( is_array( $allowed_attr[ $name_low ] ) ) {
+		// There are some checks.
+		foreach ( $allowed_attr[ $name_low ] as $currkey => $currval ) {
+			if ( ! wp_kses_check_attr_val( $value, $vless, $currkey, $currval ) ) {
+				$name  = '';
+				$value = '';
+				$whole = '';
+				return false;
+			}
+		}
+	}
+
+	return true;
+}
+
 /**
  * Builds an attribute list from string containing attributes.
  *
@@ -632,238 +1267,391 @@ function wp_kses_attr($element, $attr, $allowed_html, $allowed_protocols) {
  * or apostrophes around them, to make it easier to produce HTML code that will
  * conform to W3C's HTML specification. It will also remove bad URL protocols
  * from attribute values. It also reduces duplicate attributes by using the
- * attribute defined first (foo='bar' foo='baz' will result in foo='bar').
+ * attribute defined first (`foo='bar' foo='baz'` will result in `foo='bar'`).
  *
  * @since 1.0.0
  *
- * @param string $attr Attribute list from HTML element to closing HTML element tag
- * @param array $allowed_protocols Allowed protocols to keep
- * @return array List of attributes after parsing
+ * @param string   $attr              Attribute list from HTML element to closing HTML element tag.
+ * @param string[] $allowed_protocols Array of allowed URL protocols.
+ * @return array[] Array of attribute information after parsing.
  */
-function wp_kses_hair($attr, $allowed_protocols) {
-	$attrarr = array();
-	$mode = 0;
+function wp_kses_hair( $attr, $allowed_protocols ) {
+	$attrarr  = array();
+	$mode     = 0;
 	$attrname = '';
-	$uris = array('xmlns', 'profile', 'href', 'src', 'cite', 'classid', 'codebase', 'data', 'usemap', 'longdesc', 'action');
+	$uris     = wp_kses_uri_attributes();
 
-	# Loop through the whole attribute list
+	// Loop through the whole attribute list.
 
-	while (strlen($attr) != 0) {
-		$working = 0; # Was the last operation successful?
+	while ( strlen( $attr ) != 0 ) {
+		$working = 0; // Was the last operation successful?
 
-		switch ($mode) {
-			case 0 : # attribute name, href for instance
-
-				if (preg_match('/^([-a-zA-Z]+)/', $attr, $match)) {
+		switch ( $mode ) {
+			case 0:
+				if ( preg_match( '/^([_a-zA-Z][-_a-zA-Z0-9:.]*)/', $attr, $match ) ) {
 					$attrname = $match[1];
-					$working = $mode = 1;
-					$attr = preg_replace('/^[-a-zA-Z]+/', '', $attr);
+					$working  = 1;
+					$mode     = 1;
+					$attr     = preg_replace( '/^[_a-zA-Z][-_a-zA-Z0-9:.]*/', '', $attr );
 				}
 
 				break;
 
-			case 1 : # equals sign or valueless ("selected")
-
-				if (preg_match('/^\s*=\s*/', $attr)) # equals sign
-					{
+			case 1:
+				if ( preg_match( '/^\s*=\s*/', $attr ) ) { // Equals sign.
 					$working = 1;
-					$mode = 2;
-					$attr = preg_replace('/^\s*=\s*/', '', $attr);
+					$mode    = 2;
+					$attr    = preg_replace( '/^\s*=\s*/', '', $attr );
 					break;
 				}
 
-				if (preg_match('/^\s+/', $attr)) # valueless
-					{
+				if ( preg_match( '/^\s+/', $attr ) ) { // Valueless.
 					$working = 1;
-					$mode = 0;
-					if(false === array_key_exists($attrname, $attrarr)) {
-						$attrarr[$attrname] = array ('name' => $attrname, 'value' => '', 'whole' => $attrname, 'vless' => 'y');
+					$mode    = 0;
+					if ( false === array_key_exists( $attrname, $attrarr ) ) {
+						$attrarr[ $attrname ] = array(
+							'name'  => $attrname,
+							'value' => '',
+							'whole' => $attrname,
+							'vless' => 'y',
+						);
 					}
-					$attr = preg_replace('/^\s+/', '', $attr);
+					$attr = preg_replace( '/^\s+/', '', $attr );
 				}
 
 				break;
 
-			case 2 : # attribute value, a URL after href= for instance
-
-				if (preg_match('%^"([^"]*)"(\s+|/?$)%', $attr, $match))
-					# "value"
-					{
+			case 2:
+				if ( preg_match( '%^"([^"]*)"(\s+|/?$)%', $attr, $match ) ) {
+					// "value"
 					$thisval = $match[1];
-					if ( in_array(strtolower($attrname), $uris) )
-						$thisval = wp_kses_bad_protocol($thisval, $allowed_protocols);
+					if ( in_array( strtolower( $attrname ), $uris, true ) ) {
+						$thisval = wp_kses_bad_protocol( $thisval, $allowed_protocols );
+					}
 
-					if(false === array_key_exists($attrname, $attrarr)) {
-						$attrarr[$attrname] = array ('name' => $attrname, 'value' => $thisval, 'whole' => "$attrname=\"$thisval\"", 'vless' => 'n');
+					if ( false === array_key_exists( $attrname, $attrarr ) ) {
+						$attrarr[ $attrname ] = array(
+							'name'  => $attrname,
+							'value' => $thisval,
+							'whole' => "$attrname=\"$thisval\"",
+							'vless' => 'n',
+						);
 					}
 					$working = 1;
-					$mode = 0;
-					$attr = preg_replace('/^"[^"]*"(\s+|$)/', '', $attr);
+					$mode    = 0;
+					$attr    = preg_replace( '/^"[^"]*"(\s+|$)/', '', $attr );
 					break;
 				}
 
-				if (preg_match("%^'([^']*)'(\s+|/?$)%", $attr, $match))
-					# 'value'
-					{
+				if ( preg_match( "%^'([^']*)'(\s+|/?$)%", $attr, $match ) ) {
+					// 'value'
 					$thisval = $match[1];
-					if ( in_array(strtolower($attrname), $uris) )
-						$thisval = wp_kses_bad_protocol($thisval, $allowed_protocols);
+					if ( in_array( strtolower( $attrname ), $uris, true ) ) {
+						$thisval = wp_kses_bad_protocol( $thisval, $allowed_protocols );
+					}
 
-					if(false === array_key_exists($attrname, $attrarr)) {
-						$attrarr[$attrname] = array ('name' => $attrname, 'value' => $thisval, 'whole' => "$attrname='$thisval'", 'vless' => 'n');
+					if ( false === array_key_exists( $attrname, $attrarr ) ) {
+						$attrarr[ $attrname ] = array(
+							'name'  => $attrname,
+							'value' => $thisval,
+							'whole' => "$attrname='$thisval'",
+							'vless' => 'n',
+						);
 					}
 					$working = 1;
-					$mode = 0;
-					$attr = preg_replace("/^'[^']*'(\s+|$)/", '', $attr);
+					$mode    = 0;
+					$attr    = preg_replace( "/^'[^']*'(\s+|$)/", '', $attr );
 					break;
 				}
 
-				if (preg_match("%^([^\s\"']+)(\s+|/?$)%", $attr, $match))
-					# value
-					{
+				if ( preg_match( "%^([^\s\"']+)(\s+|/?$)%", $attr, $match ) ) {
+					// value
 					$thisval = $match[1];
-					if ( in_array(strtolower($attrname), $uris) )
-						$thisval = wp_kses_bad_protocol($thisval, $allowed_protocols);
-
-					if(false === array_key_exists($attrname, $attrarr)) {
-						$attrarr[$attrname] = array ('name' => $attrname, 'value' => $thisval, 'whole' => "$attrname=\"$thisval\"", 'vless' => 'n');
+					if ( in_array( strtolower( $attrname ), $uris, true ) ) {
+						$thisval = wp_kses_bad_protocol( $thisval, $allowed_protocols );
 					}
-					# We add quotes to conform to W3C's HTML spec.
+
+					if ( false === array_key_exists( $attrname, $attrarr ) ) {
+						$attrarr[ $attrname ] = array(
+							'name'  => $attrname,
+							'value' => $thisval,
+							'whole' => "$attrname=\"$thisval\"",
+							'vless' => 'n',
+						);
+					}
+					// We add quotes to conform to W3C's HTML spec.
 					$working = 1;
-					$mode = 0;
-					$attr = preg_replace("%^[^\s\"']+(\s+|$)%", '', $attr);
+					$mode    = 0;
+					$attr    = preg_replace( "%^[^\s\"']+(\s+|$)%", '', $attr );
 				}
 
 				break;
-		} # switch
+		} // End switch.
 
-		if ($working == 0) # not well formed, remove and try again
-		{
-			$attr = wp_kses_html_error($attr);
+		if ( 0 == $working ) { // Not well-formed, remove and try again.
+			$attr = wp_kses_html_error( $attr );
 			$mode = 0;
 		}
-	} # while
+	} // End while.
 
-	if ($mode == 1 && false === array_key_exists($attrname, $attrarr))
-		# special case, for when the attribute list ends with a valueless
-		# attribute like "selected"
-		$attrarr[$attrname] = array ('name' => $attrname, 'value' => '', 'whole' => $attrname, 'vless' => 'y');
+	if ( 1 == $mode && false === array_key_exists( $attrname, $attrarr ) ) {
+		// Special case, for when the attribute list ends with a valueless
+		// attribute like "selected".
+		$attrarr[ $attrname ] = array(
+			'name'  => $attrname,
+			'value' => '',
+			'whole' => $attrname,
+			'vless' => 'y',
+		);
+	}
 
 	return $attrarr;
 }
 
+/**
+ * Finds all attributes of an HTML element.
+ *
+ * Does not modify input.  May return "evil" output.
+ *
+ * Based on `wp_kses_split2()` and `wp_kses_attr()`.
+ *
+ * @since 4.2.3
+ *
+ * @param string $element HTML element.
+ * @return array|false List of attributes found in the element. Returns false on failure.
+ */
+function wp_kses_attr_parse( $element ) {
+	$valid = preg_match( '%^(<\s*)(/\s*)?([a-zA-Z0-9]+\s*)([^>]*)(>?)$%', $element, $matches );
+	if ( 1 !== $valid ) {
+		return false;
+	}
+
+	$begin  = $matches[1];
+	$slash  = $matches[2];
+	$elname = $matches[3];
+	$attr   = $matches[4];
+	$end    = $matches[5];
+
+	if ( '' !== $slash ) {
+		// Closing elements do not get parsed.
+		return false;
+	}
+
+	// Is there a closing XHTML slash at the end of the attributes?
+	if ( 1 === preg_match( '%\s*/\s*$%', $attr, $matches ) ) {
+		$xhtml_slash = $matches[0];
+		$attr        = substr( $attr, 0, -strlen( $xhtml_slash ) );
+	} else {
+		$xhtml_slash = '';
+	}
+
+	// Split it.
+	$attrarr = wp_kses_hair_parse( $attr );
+	if ( false === $attrarr ) {
+		return false;
+	}
+
+	// Make sure all input is returned by adding front and back matter.
+	array_unshift( $attrarr, $begin . $slash . $elname );
+	array_push( $attrarr, $xhtml_slash . $end );
+
+	return $attrarr;
+}
+
+/**
+ * Builds an attribute list from string containing attributes.
+ *
+ * Does not modify input.  May return "evil" output.
+ * In case of unexpected input, returns false instead of stripping things.
+ *
+ * Based on `wp_kses_hair()` but does not return a multi-dimensional array.
+ *
+ * @since 4.2.3
+ *
+ * @param string $attr Attribute list from HTML element to closing HTML element tag.
+ * @return array|false List of attributes found in $attr. Returns false on failure.
+ */
+function wp_kses_hair_parse( $attr ) {
+	if ( '' === $attr ) {
+		return array();
+	}
+
+	// phpcs:disable Squiz.Strings.ConcatenationSpacing.PaddingFound -- don't remove regex indentation
+	$regex =
+		'(?:'
+		.     '[_a-zA-Z][-_a-zA-Z0-9:.]*' // Attribute name.
+		. '|'
+		.     '\[\[?[^\[\]]+\]\]?'        // Shortcode in the name position implies unfiltered_html.
+		. ')'
+		. '(?:'               // Attribute value.
+		.     '\s*=\s*'       // All values begin with '='.
+		.     '(?:'
+		.         '"[^"]*"'   // Double-quoted.
+		.     '|'
+		.         "'[^']*'"   // Single-quoted.
+		.     '|'
+		.         '[^\s"\']+' // Non-quoted.
+		.         '(?:\s|$)'  // Must have a space.
+		.     ')'
+		. '|'
+		.     '(?:\s|$)'      // If attribute has no value, space is required.
+		. ')'
+		. '\s*';              // Trailing space is optional except as mentioned above.
+	// phpcs:enable
+
+	// Although it is possible to reduce this procedure to a single regexp,
+	// we must run that regexp twice to get exactly the expected result.
+
+	$validation = "%^($regex)+$%";
+	$extraction = "%$regex%";
+
+	if ( 1 === preg_match( $validation, $attr ) ) {
+		preg_match_all( $extraction, $attr, $attrarr );
+		return $attrarr[0];
+	} else {
+		return false;
+	}
+}
+
 /**
  * Performs different checks for attribute values.
  *
- * The currently implemented checks are "maxlen", "minlen", "maxval", "minval"
+ * The currently implemented checks are "maxlen", "minlen", "maxval", "minval",
  * and "valueless".
  *
  * @since 1.0.0
  *
- * @param string $value Attribute value
- * @param string $vless Whether the value is valueless. Use 'y' or 'n'
- * @param string $checkname What $checkvalue is checking for.
- * @param mixed $checkvalue What constraint the value should pass
- * @return bool Whether check passes
+ * @param string $value      Attribute value.
+ * @param string $vless      Whether the attribute is valueless. Use 'y' or 'n'.
+ * @param string $checkname  What $checkvalue is checking for.
+ * @param mixed  $checkvalue What constraint the value should pass.
+ * @return bool Whether check passes.
  */
-function wp_kses_check_attr_val($value, $vless, $checkname, $checkvalue) {
+function wp_kses_check_attr_val( $value, $vless, $checkname, $checkvalue ) {
 	$ok = true;
 
-	switch (strtolower($checkname)) {
-		case 'maxlen' :
-			# The maxlen check makes sure that the attribute value has a length not
-			# greater than the given value. This can be used to avoid Buffer Overflows
-			# in WWW clients and various Internet servers.
+	switch ( strtolower( $checkname ) ) {
+		case 'maxlen':
+			/*
+			 * The maxlen check makes sure that the attribute value has a length not
+			 * greater than the given value. This can be used to avoid Buffer Overflows
+			 * in WWW clients and various Internet servers.
+			 */
 
-			if (strlen($value) > $checkvalue)
+			if ( strlen( $value ) > $checkvalue ) {
 				$ok = false;
+			}
 			break;
 
-		case 'minlen' :
-			# The minlen check makes sure that the attribute value has a length not
-			# smaller than the given value.
+		case 'minlen':
+			/*
+			 * The minlen check makes sure that the attribute value has a length not
+			 * smaller than the given value.
+			 */
 
-			if (strlen($value) < $checkvalue)
+			if ( strlen( $value ) < $checkvalue ) {
 				$ok = false;
+			}
 			break;
 
-		case 'maxval' :
-			# The maxval check does two things: it checks that the attribute value is
-			# an integer from 0 and up, without an excessive amount of zeroes or
-			# whitespace (to avoid Buffer Overflows). It also checks that the attribute
-			# value is not greater than the given value.
-			# This check can be used to avoid Denial of Service attacks.
+		case 'maxval':
+			/*
+			 * The maxval check does two things: it checks that the attribute value is
+			 * an integer from 0 and up, without an excessive amount of zeroes or
+			 * whitespace (to avoid Buffer Overflows). It also checks that the attribute
+			 * value is not greater than the given value.
+			 * This check can be used to avoid Denial of Service attacks.
+			 */
 
-			if (!preg_match('/^\s{0,6}[0-9]{1,6}\s{0,6}$/', $value))
+			if ( ! preg_match( '/^\s{0,6}[0-9]{1,6}\s{0,6}$/', $value ) ) {
 				$ok = false;
-			if ($value > $checkvalue)
+			}
+			if ( $value > $checkvalue ) {
 				$ok = false;
+			}
 			break;
 
-		case 'minval' :
-			# The minval check makes sure that the attribute value is a positive integer,
-			# and that it is not smaller than the given value.
+		case 'minval':
+			/*
+			 * The minval check makes sure that the attribute value is a positive integer,
+			 * and that it is not smaller than the given value.
+			 */
 
-			if (!preg_match('/^\s{0,6}[0-9]{1,6}\s{0,6}$/', $value))
+			if ( ! preg_match( '/^\s{0,6}[0-9]{1,6}\s{0,6}$/', $value ) ) {
 				$ok = false;
-			if ($value < $checkvalue)
+			}
+			if ( $value < $checkvalue ) {
 				$ok = false;
+			}
 			break;
 
-		case 'valueless' :
-			# The valueless check makes sure if the attribute has a value
-			# (like <a href="blah">) or not (<option selected>). If the given value
-			# is a "y" or a "Y", the attribute must not have a value.
-			# If the given value is an "n" or an "N", the attribute must have one.
+		case 'valueless':
+			/*
+			 * The valueless check makes sure if the attribute has a value
+			 * (like `<a href="blah">`) or not (`<option selected>`). If the given value
+			 * is a "y" or a "Y", the attribute must not have a value.
+			 * If the given value is an "n" or an "N", the attribute must have a value.
+			 */
 
-			if (strtolower($checkvalue) != $vless)
+			if ( strtolower( $checkvalue ) != $vless ) {
 				$ok = false;
+			}
 			break;
-	} # switch
+	} // End switch.
 
 	return $ok;
 }
 
 /**
- * Sanitize string from bad protocols.
+ * Sanitizes a string and removed disallowed URL protocols.
  *
- * This function removes all non-allowed protocols from the beginning of
- * $string. It ignores whitespace and the case of the letters, and it does
- * understand HTML entities. It does its work in a while loop, so it won't be
- * fooled by a string like "javascript:javascript:alert(57)".
+ * This function removes all non-allowed protocols from the beginning of the
+ * string. It ignores whitespace and the case of the letters, and it does
+ * understand HTML entities. It does its work recursively, so it won't be
+ * fooled by a string like `javascript:javascript:alert(57)`.
  *
  * @since 1.0.0
  *
- * @param string $string Content to filter bad protocols from
- * @param array $allowed_protocols Allowed protocols to keep
- * @return string Filtered content
+ * @param string   $string            Content to filter bad protocols from.
+ * @param string[] $allowed_protocols Array of allowed URL protocols.
+ * @return string Filtered content.
  */
-function wp_kses_bad_protocol($string, $allowed_protocols) {
-	$string = wp_kses_no_null($string);
+function wp_kses_bad_protocol( $string, $allowed_protocols ) {
+	$string     = wp_kses_no_null( $string );
 	$iterations = 0;
 
 	do {
 		$original_string = $string;
-		$string = wp_kses_bad_protocol_once($string, $allowed_protocols);
+		$string          = wp_kses_bad_protocol_once( $string, $allowed_protocols );
 	} while ( $original_string != $string && ++$iterations < 6 );
 
-	if ( $original_string != $string )
+	if ( $original_string != $string ) {
 		return '';
+	}
 
 	return $string;
 }
 
 /**
- * Removes any null characters in $string.
+ * Removes any invalid control characters in a text string.
+ *
+ * Also removes any instance of the `\0` string.
  *
  * @since 1.0.0
  *
- * @param string $string
- * @return string
+ * @param string $string  Content to filter null characters from.
+ * @param array  $options Set 'slash_zero' => 'keep' when '\0' is allowed. Default is 'remove'.
+ * @return string Filtered content.
  */
-function wp_kses_no_null($string) {
-	$string = preg_replace('/\0+/', '', $string);
-	$string = preg_replace('/(\\\\0)+/', '', $string);
+function wp_kses_no_null( $string, $options = null ) {
+	if ( ! isset( $options['slash_zero'] ) ) {
+		$options = array( 'slash_zero' => 'remove' );
+	}
+
+	$string = preg_replace( '/[\x00-\x08\x0B\x0C\x0E-\x1F]/', '', $string );
+	if ( 'remove' === $options['slash_zero'] ) {
+		$string = preg_replace( '/\\\\+0+/', '', $string );
+	}
 
 	return $string;
 }
@@ -871,57 +1659,44 @@ function wp_kses_no_null($string) {
 /**
  * Strips slashes from in front of quotes.
  *
- * This function changes the character sequence \" to just ". It leaves all
- * other slashes alone. It's really weird, but the quoting from
- * preg_replace(//e) seems to require this.
+ * This function changes the character sequence `\"` to just `"`. It leaves all other
+ * slashes alone. The quoting from `preg_replace(//e)` requires this.
  *
  * @since 1.0.0
  *
- * @param string $string String to strip slashes
- * @return string Fixed string with quoted slashes
+ * @param string $string String to strip slashes from.
+ * @return string Fixed string with quoted slashes.
  */
-function wp_kses_stripslashes($string) {
-	return preg_replace('%\\\\"%', '"', $string);
+function wp_kses_stripslashes( $string ) {
+	return preg_replace( '%\\\\"%', '"', $string );
 }
 
 /**
- * Goes through an array and changes the keys to all lower case.
+ * Converts the keys of an array to lowercase.
  *
  * @since 1.0.0
  *
- * @param array $inarray Unfiltered array
- * @return array Fixed array with all lowercase keys
+ * @param array $inarray Unfiltered array.
+ * @return array Fixed array with all lowercase keys.
  */
-function wp_kses_array_lc($inarray) {
-	$outarray = array ();
+function wp_kses_array_lc( $inarray ) {
+	$outarray = array();
 
-	foreach ( (array) $inarray as $inkey => $inval) {
-		$outkey = strtolower($inkey);
-		$outarray[$outkey] = array ();
+	foreach ( (array) $inarray as $inkey => $inval ) {
+		$outkey              = strtolower( $inkey );
+		$outarray[ $outkey ] = array();
 
-		foreach ( (array) $inval as $inkey2 => $inval2) {
-			$outkey2 = strtolower($inkey2);
-			$outarray[$outkey][$outkey2] = $inval2;
-		} # foreach $inval
-	} # foreach $inarray
+		foreach ( (array) $inval as $inkey2 => $inval2 ) {
+			$outkey2                         = strtolower( $inkey2 );
+			$outarray[ $outkey ][ $outkey2 ] = $inval2;
+		}
+	}
 
 	return $outarray;
 }
 
 /**
- * Removes the HTML JavaScript entities found in early versions of Netscape 4.
- *
- * @since 1.0.0
- *
- * @param string $string
- * @return string
- */
-function wp_kses_js_entities($string) {
-	return preg_replace('%&\s*\{[^}]*(\}\s*;?|$)%', '', $string);
-}
-
-/**
- * Handles parsing errors in wp_kses_hair().
+ * Handles parsing errors in `wp_kses_hair()`.
  *
  * The general plan is to remove everything to and including some whitespace,
  * but it deals with quotes and apostrophes as well.
@@ -931,33 +1706,37 @@ function wp_kses_js_entities($string) {
  * @param string $string
  * @return string
  */
-function wp_kses_html_error($string) {
-	return preg_replace('/^("[^"]*("|$)|\'[^\']*(\'|$)|\S)*\s*/', '', $string);
+function wp_kses_html_error( $string ) {
+	return preg_replace( '/^("[^"]*("|$)|\'[^\']*(\'|$)|\S)*\s*/', '', $string );
 }
 
 /**
  * Sanitizes content from bad protocols and other characters.
  *
- * This function searches for URL protocols at the beginning of $string, while
+ * This function searches for URL protocols at the beginning of the string, while
  * handling whitespace and HTML entities.
  *
  * @since 1.0.0
  *
- * @param string $string Content to check for bad protocols
- * @param string $allowed_protocols Allowed protocols
- * @return string Sanitized content
+ * @param string   $string            Content to check for bad protocols.
+ * @param string[] $allowed_protocols Array of allowed URL protocols.
+ * @param int      $count             Depth of call recursion to this function.
+ * @return string Sanitized content.
  */
-function wp_kses_bad_protocol_once($string, $allowed_protocols, $count = 1 ) {
-	$string2 = preg_split( '/:|&#0*58;|&#x0*3a;/i', $string, 2 );
-	if ( isset($string2[1]) && ! preg_match('%/\?%', $string2[0]) ) {
-		$string = trim( $string2[1] );
+function wp_kses_bad_protocol_once( $string, $allowed_protocols, $count = 1 ) {
+	$string  = preg_replace( '/(&#0*58(?![;0-9])|&#x0*3a(?![;a-f0-9]))/i', '$1;', $string );
+	$string2 = preg_split( '/:|&#0*58;|&#x0*3a;|&colon;/i', $string, 2 );
+	if ( isset( $string2[1] ) && ! preg_match( '%/\?%', $string2[0] ) ) {
+		$string   = trim( $string2[1] );
 		$protocol = wp_kses_bad_protocol_once2( $string2[0], $allowed_protocols );
-		if ( 'feed:' == $protocol ) {
-			if ( $count > 2 )
+		if ( 'feed:' === $protocol ) {
+			if ( $count > 2 ) {
 				return '';
+			}
 			$string = wp_kses_bad_protocol_once( $string, $allowed_protocols, ++$count );
-			if ( empty( $string ) )
+			if ( empty( $string ) ) {
 				return $string;
+			}
 		}
 		$string = $protocol . $string;
 	}
@@ -966,102 +1745,152 @@ function wp_kses_bad_protocol_once($string, $allowed_protocols, $count = 1 ) {
 }
 
 /**
- * Callback for wp_kses_bad_protocol_once() regular expression.
+ * Callback for `wp_kses_bad_protocol_once()` regular expression.
  *
  * This function processes URL protocols, checks to see if they're in the
- * whitelist or not, and returns different data depending on the answer.
+ * list of allowed protocols or not, and returns different data depending
+ * on the answer.
  *
  * @access private
+ * @ignore
  * @since 1.0.0
  *
- * @param string $string URI scheme to check against the whitelist
- * @param string $allowed_protocols Allowed protocols
- * @return string Sanitized content
+ * @param string   $string            URI scheme to check against the list of allowed protocols.
+ * @param string[] $allowed_protocols Array of allowed URL protocols.
+ * @return string Sanitized content.
  */
 function wp_kses_bad_protocol_once2( $string, $allowed_protocols ) {
-	$string2 = wp_kses_decode_entities($string);
-	$string2 = preg_replace('/\s/', '', $string2);
-	$string2 = wp_kses_no_null($string2);
-	$string2 = strtolower($string2);
+	$string2 = wp_kses_decode_entities( $string );
+	$string2 = preg_replace( '/\s/', '', $string2 );
+	$string2 = wp_kses_no_null( $string2 );
+	$string2 = strtolower( $string2 );
 
 	$allowed = false;
-	foreach ( (array) $allowed_protocols as $one_protocol )
-		if ( strtolower($one_protocol) == $string2 ) {
+	foreach ( (array) $allowed_protocols as $one_protocol ) {
+		if ( strtolower( $one_protocol ) == $string2 ) {
 			$allowed = true;
 			break;
 		}
+	}
 
-	if ($allowed)
+	if ( $allowed ) {
 		return "$string2:";
-	else
+	} else {
 		return '';
+	}
 }
 
 /**
  * Converts and fixes HTML entities.
  *
- * This function normalizes HTML entities. It will convert "AT&T" to the correct
- * "AT&amp;T", "&#00058;" to "&#58;", "&#XYZZY;" to "&amp;#XYZZY;" and so on.
+ * This function normalizes HTML entities. It will convert `AT&T` to the correct
+ * `AT&amp;T`, `&#00058;` to `&#058;`, `&#XYZZY;` to `&amp;#XYZZY;` and so on.
+ *
+ * When `$context` is set to 'xml', HTML entities are converted to their code points.  For
+ * example, `AT&T&hellip;&#XYZZY;` is converted to `AT&amp;T…&amp;#XYZZY;`.
  *
  * @since 1.0.0
+ * @since 5.5.0 Added `$context` parameter.
  *
- * @param string $string Content to normalize entities
- * @return string Content with normalized entities
+ * @param string $string  Content to normalize entities.
+ * @param string $context Context for normalization. Can be either 'html' or 'xml'.
+ *                        Default 'html'.
+ * @return string Content with normalized entities.
  */
-function wp_kses_normalize_entities($string) {
-	# Disarm all entities by converting & to &amp;
+function wp_kses_normalize_entities( $string, $context = 'html' ) {
+	// Disarm all entities by converting & to &amp;
+	$string = str_replace( '&', '&amp;', $string );
 
-	$string = str_replace('&', '&amp;', $string);
-
-	# Change back the allowed entities in our entity whitelist
-
-	$string = preg_replace_callback('/&amp;([A-Za-z]{2,8});/', 'wp_kses_named_entities', $string);
-	$string = preg_replace_callback('/&amp;#(0*[0-9]{1,7});/', 'wp_kses_normalize_entities2', $string);
-	$string = preg_replace_callback('/&amp;#[Xx](0*[0-9A-Fa-f]{1,6});/', 'wp_kses_normalize_entities3', $string);
+	// Change back the allowed entities in our list of allowed entities.
+	if ( 'xml' === $context ) {
+		$string = preg_replace_callback( '/&amp;([A-Za-z]{2,8}[0-9]{0,2});/', 'wp_kses_xml_named_entities', $string );
+	} else {
+		$string = preg_replace_callback( '/&amp;([A-Za-z]{2,8}[0-9]{0,2});/', 'wp_kses_named_entities', $string );
+	}
+	$string = preg_replace_callback( '/&amp;#(0*[0-9]{1,7});/', 'wp_kses_normalize_entities2', $string );
+	$string = preg_replace_callback( '/&amp;#[Xx](0*[0-9A-Fa-f]{1,6});/', 'wp_kses_normalize_entities3', $string );
 
 	return $string;
 }
 
 /**
- * Callback for wp_kses_normalize_entities() regular expression.
+ * Callback for `wp_kses_normalize_entities()` regular expression.
  *
  * This function only accepts valid named entity references, which are finite,
  * case-sensitive, and highly scrutinized by HTML and XML validators.
  *
  * @since 3.0.0
  *
- * @param array $matches preg_replace_callback() matches array
- * @return string Correctly encoded entity
+ * @global array $allowedentitynames
+ *
+ * @param array $matches preg_replace_callback() matches array.
+ * @return string Correctly encoded entity.
  */
-function wp_kses_named_entities($matches) {
+function wp_kses_named_entities( $matches ) {
 	global $allowedentitynames;
 
-	if ( empty($matches[1]) )
+	if ( empty( $matches[1] ) ) {
 		return '';
+	}
 
 	$i = $matches[1];
-	return ( ( ! in_array($i, $allowedentitynames) ) ? "&amp;$i;" : "&$i;" );
+	return ( ! in_array( $i, $allowedentitynames, true ) ) ? "&amp;$i;" : "&$i;";
 }
 
 /**
- * Callback for wp_kses_normalize_entities() regular expression.
+ * Callback for `wp_kses_normalize_entities()` regular expression.
  *
- * This function helps wp_kses_normalize_entities() to only accept 16-bit values
- * and nothing more for &#number; entities.
+ * This function only accepts valid named entity references, which are finite,
+ * case-sensitive, and highly scrutinized by XML validators.  HTML named entity
+ * references are converted to their code points.
  *
- * @access private
- * @since 1.0.0
+ * @since 5.5.0
  *
- * @param array $matches preg_replace_callback() matches array
- * @return string Correctly encoded entity
+ * @global array $allowedentitynames
+ * @global array $allowedxmlnamedentities
+ *
+ * @param array $matches preg_replace_callback() matches array.
+ * @return string Correctly encoded entity.
  */
-function wp_kses_normalize_entities2($matches) {
-	if ( empty($matches[1]) )
+function wp_kses_xml_named_entities( $matches ) {
+	global $allowedentitynames, $allowedxmlnamedentities;
+
+	if ( empty( $matches[1] ) ) {
 		return '';
+	}
 
 	$i = $matches[1];
-	if (valid_unicode($i)) {
-		$i = str_pad(ltrim($i,'0'), 3, '0', STR_PAD_LEFT);
+
+	if ( in_array( $i, $allowedxmlnamedentities, true ) ) {
+		return "&$i;";
+	} elseif ( in_array( $i, $allowedentitynames, true ) ) {
+		return html_entity_decode( "&$i;", ENT_HTML5 );
+	}
+
+	return "&amp;$i;";
+}
+
+/**
+ * Callback for `wp_kses_normalize_entities()` regular expression.
+ *
+ * This function helps `wp_kses_normalize_entities()` to only accept 16-bit
+ * values and nothing more for `&#number;` entities.
+ *
+ * @access private
+ * @ignore
+ * @since 1.0.0
+ *
+ * @param array $matches `preg_replace_callback()` matches array.
+ * @return string Correctly encoded entity.
+ */
+function wp_kses_normalize_entities2( $matches ) {
+	if ( empty( $matches[1] ) ) {
+		return '';
+	}
+
+	$i = $matches[1];
+	if ( valid_unicode( $i ) ) {
+		$i = str_pad( ltrim( $i, '0' ), 3, '0', STR_PAD_LEFT );
 		$i = "&#$i;";
 	} else {
 		$i = "&amp;#$i;";
@@ -1071,58 +1900,67 @@ function wp_kses_normalize_entities2($matches) {
 }
 
 /**
- * Callback for wp_kses_normalize_entities() for regular expression.
+ * Callback for `wp_kses_normalize_entities()` for regular expression.
  *
- * This function helps wp_kses_normalize_entities() to only accept valid Unicode
+ * This function helps `wp_kses_normalize_entities()` to only accept valid Unicode
  * numeric entities in hex form.
  *
+ * @since 2.7.0
  * @access private
+ * @ignore
  *
- * @param array $matches preg_replace_callback() matches array
- * @return string Correctly encoded entity
+ * @param array $matches `preg_replace_callback()` matches array.
+ * @return string Correctly encoded entity.
  */
-function wp_kses_normalize_entities3($matches) {
-	if ( empty($matches[1]) )
+function wp_kses_normalize_entities3( $matches ) {
+	if ( empty( $matches[1] ) ) {
 		return '';
+	}
 
 	$hexchars = $matches[1];
-	return ( ( ! valid_unicode(hexdec($hexchars)) ) ? "&amp;#x$hexchars;" : '&#x'.ltrim($hexchars,'0').';' );
+	return ( ! valid_unicode( hexdec( $hexchars ) ) ) ? "&amp;#x$hexchars;" : '&#x' . ltrim( $hexchars, '0' ) . ';';
 }
 
 /**
- * Helper function to determine if a Unicode value is valid.
+ * Determines if a Unicode codepoint is valid.
  *
- * @param int $i Unicode value
- * @return bool True if the value was a valid Unicode number
+ * @since 2.7.0
+ *
+ * @param int $i Unicode codepoint.
+ * @return bool Whether or not the codepoint is a valid Unicode codepoint.
  */
-function valid_unicode($i) {
-	return ( $i == 0x9 || $i == 0xa || $i == 0xd ||
-			($i >= 0x20 && $i <= 0xd7ff) ||
-			($i >= 0xe000 && $i <= 0xfffd) ||
-			($i >= 0x10000 && $i <= 0x10ffff) );
+function valid_unicode( $i ) {
+	return ( 0x9 == $i || 0xa == $i || 0xd == $i ||
+			( 0x20 <= $i && $i <= 0xd7ff ) ||
+			( 0xe000 <= $i && $i <= 0xfffd ) ||
+			( 0x10000 <= $i && $i <= 0x10ffff ) );
 }
 
 /**
- * Convert all entities to their character counterparts.
+ * Converts all numeric HTML entities to their named counterparts.
  *
- * This function decodes numeric HTML entities (&#65; and &#x41;). It doesn't do
- * anything with other entities like &auml;, but we don't need them in the URL
- * protocol whitelisting system anyway.
+ * This function decodes numeric HTML entities (`&#65;` and `&#x41;`).
+ * It doesn't do anything with named entities like `&auml;`, but we don't
+ * need them in the allowed URL protocols system anyway.
  *
  * @since 1.0.0
  *
- * @param string $string Content to change entities
- * @return string Content after decoded entities
+ * @param string $string Content to change entities.
+ * @return string Content after decoded entities.
  */
-function wp_kses_decode_entities($string) {
-	$string = preg_replace_callback('/&#([0-9]+);/', '_wp_kses_decode_entities_chr', $string);
-	$string = preg_replace_callback('/&#[Xx]([0-9A-Fa-f]+);/', '_wp_kses_decode_entities_chr_hexdec', $string);
+function wp_kses_decode_entities( $string ) {
+	$string = preg_replace_callback( '/&#([0-9]+);/', '_wp_kses_decode_entities_chr', $string );
+	$string = preg_replace_callback( '/&#[Xx]([0-9A-Fa-f]+);/', '_wp_kses_decode_entities_chr_hexdec', $string );
 
 	return $string;
 }
 
 /**
- * Regex callback for wp_kses_decode_entities()
+ * Regex callback for `wp_kses_decode_entities()`.
+ *
+ * @since 2.9.0
+ * @access private
+ * @ignore
  *
  * @param array $match preg match
  * @return string
@@ -1132,7 +1970,11 @@ function _wp_kses_decode_entities_chr( $match ) {
 }
 
 /**
- * Regex callback for wp_kses_decode_entities()
+ * Regex callback for `wp_kses_decode_entities()`.
+ *
+ * @since 2.9.0
+ * @access private
+ * @ignore
  *
  * @param array $match preg match
  * @return string
@@ -1141,59 +1983,443 @@ function _wp_kses_decode_entities_chr_hexdec( $match ) {
 	return chr( hexdec( $match[1] ) );
 }
 
-
+/**
+ * Sanitize content with allowed HTML KSES rules.
+ *
+ * This function expects slashed data.
+ *
+ * @since 1.0.0
+ *
+ * @param string $data Content to filter, expected to be escaped with slashes.
+ * @return string Filtered content.
+ */
+function wp_filter_kses( $data ) {
+	return addslashes( wp_kses( stripslashes( $data ), current_filter() ) );
+}
 
 /**
- * Inline CSS filter
+ * Sanitize content with allowed HTML KSES rules.
+ *
+ * This function expects unslashed data.
+ *
+ * @since 2.9.0
+ *
+ * @param string $data Content to filter, expected to not be escaped.
+ * @return string Filtered content.
+ */
+function wp_kses_data( $data ) {
+	return wp_kses( $data, current_filter() );
+}
+
+/**
+ * Sanitizes content for allowed HTML tags for post content.
+ *
+ * Post content refers to the page contents of the 'post' type and not `$_POST`
+ * data from forms.
+ *
+ * This function expects slashed data.
+ *
+ * @since 2.0.0
+ *
+ * @param string $data Post content to filter, expected to be escaped with slashes.
+ * @return string Filtered post content with allowed HTML tags and attributes intact.
+ */
+function wp_filter_post_kses( $data ) {
+	return addslashes( wp_kses( stripslashes( $data ), 'post' ) );
+}
+
+/**
+ * Sanitizes content for allowed HTML tags for post content.
+ *
+ * Post content refers to the page contents of the 'post' type and not `$_POST`
+ * data from forms.
+ *
+ * This function expects unslashed data.
+ *
+ * @since 2.9.0
+ *
+ * @param string $data Post content to filter.
+ * @return string Filtered post content with allowed HTML tags and attributes intact.
+ */
+function wp_kses_post( $data ) {
+	return wp_kses( $data, 'post' );
+}
+
+/**
+ * Navigates through an array, object, or scalar, and sanitizes content for
+ * allowed HTML tags for post content.
+ *
+ * @since 4.4.2
+ *
+ * @see map_deep()
+ *
+ * @param mixed $data The array, object, or scalar value to inspect.
+ * @return mixed The filtered content.
+ */
+function wp_kses_post_deep( $data ) {
+	return map_deep( $data, 'wp_kses_post' );
+}
+
+/**
+ * Strips all HTML from a text string.
+ *
+ * This function expects slashed data.
+ *
+ * @since 2.1.0
+ *
+ * @param string $data Content to strip all HTML from.
+ * @return string Filtered content without any HTML.
+ */
+function wp_filter_nohtml_kses( $data ) {
+	return addslashes( wp_kses( stripslashes( $data ), 'strip' ) );
+}
+
+/**
+ * Adds all KSES input form content filters.
+ *
+ * All hooks have default priority. The `wp_filter_kses()` function is added to
+ * the 'pre_comment_content' and 'title_save_pre' hooks.
+ *
+ * The `wp_filter_post_kses()` function is added to the 'content_save_pre',
+ * 'excerpt_save_pre', and 'content_filtered_save_pre' hooks.
+ *
+ * @since 2.0.0
+ */
+function kses_init_filters() {
+	// Normal filtering.
+	add_filter( 'title_save_pre', 'wp_filter_kses' );
+
+	// Comment filtering.
+	if ( current_user_can( 'unfiltered_html' ) ) {
+		add_filter( 'pre_comment_content', 'wp_filter_post_kses' );
+	} else {
+		add_filter( 'pre_comment_content', 'wp_filter_kses' );
+	}
+
+	// Post filtering.
+	add_filter( 'content_save_pre', 'wp_filter_post_kses' );
+	add_filter( 'excerpt_save_pre', 'wp_filter_post_kses' );
+	add_filter( 'content_filtered_save_pre', 'wp_filter_post_kses' );
+}
+
+/**
+ * Removes all KSES input form content filters.
+ *
+ * A quick procedural method to removing all of the filters that KSES uses for
+ * content in WordPress Loop.
+ *
+ * Does not remove the `kses_init()` function from {@see 'init'} hook (priority is
+ * default). Also does not remove `kses_init()` function from {@see 'set_current_user'}
+ * hook (priority is also default).
+ *
+ * @since 2.0.6
+ */
+function kses_remove_filters() {
+	// Normal filtering.
+	remove_filter( 'title_save_pre', 'wp_filter_kses' );
+
+	// Comment filtering.
+	remove_filter( 'pre_comment_content', 'wp_filter_post_kses' );
+	remove_filter( 'pre_comment_content', 'wp_filter_kses' );
+
+	// Post filtering.
+	remove_filter( 'content_save_pre', 'wp_filter_post_kses' );
+	remove_filter( 'excerpt_save_pre', 'wp_filter_post_kses' );
+	remove_filter( 'content_filtered_save_pre', 'wp_filter_post_kses' );
+}
+
+/**
+ * Sets up most of the KSES filters for input form content.
+ *
+ * First removes all of the KSES filters in case the current user does not need
+ * to have KSES filter the content. If the user does not have `unfiltered_html`
+ * capability, then KSES filters are added.
+ *
+ * @since 2.0.0
+ */
+function kses_init() {
+	kses_remove_filters();
+
+	if ( ! current_user_can( 'unfiltered_html' ) ) {
+		kses_init_filters();
+	}
+}
+
+/**
+ * Filters an inline style attribute and removes disallowed rules.
  *
  * @since 2.8.1
+ *
+ * @param string $css        A string of CSS rules.
+ * @param string $deprecated Not used.
+ * @return string Filtered string of CSS rules.
  */
 function safecss_filter_attr( $css, $deprecated = '' ) {
-	if ( !empty( $deprecated ) )
-		_deprecated_argument( __FUNCTION__, '2.8.1' ); // Never implemented
+	if ( ! empty( $deprecated ) ) {
+		_deprecated_argument( __FUNCTION__, '2.8.1' ); // Never implemented.
+	}
 
-	$css = wp_kses_no_null($css);
-	$css = str_replace(array("\n","\r","\t"), '', $css);
+	$css = wp_kses_no_null( $css );
+	$css = str_replace( array( "\n", "\r", "\t" ), '', $css );
 
-	if ( preg_match( '%[\\(&=}]|/\*%', $css ) ) // remove any inline css containing \ ( & } = or comments
-		return '';
+	$allowed_protocols = wp_allowed_protocols();
 
 	$css_array = explode( ';', trim( $css ) );
 
-	/*
-	$allowed_attr = apply_filters( 'safe_style_css', array( 'text-align', 'margin', 'color', 'float',
-	'border', 'background', 'background-color', 'border-bottom', 'border-bottom-color',
-	'border-bottom-style', 'border-bottom-width', 'border-collapse', 'border-color', 'border-left',
-	'border-left-color', 'border-left-style', 'border-left-width', 'border-right', 'border-right-color',
-	'border-right-style', 'border-right-width', 'border-spacing', 'border-style', 'border-top',
-	'border-top-color', 'border-top-style', 'border-top-width', 'border-width', 'caption-side',
-	'clear', 'cursor', 'direction', 'font', 'font-family', 'font-size', 'font-style',
-	'font-variant', 'font-weight', 'height', 'letter-spacing', 'line-height', 'margin-bottom',
-	'margin-left', 'margin-right', 'margin-top', 'overflow', 'padding', 'padding-bottom',
-	'padding-left', 'padding-right', 'padding-top', 'text-decoration', 'text-indent', 'vertical-align',
-	'width' ) );
-	*/
+	/**
+	 * Filters list of allowed CSS attributes.
+	 *
+	 * @since 2.8.1
+	 * @since 4.4.0 Added support for `min-height`, `max-height`, `min-width`, and `max-width`.
+	 * @since 4.6.0 Added support for `list-style-type`.
+	 * @since 5.0.0 Added support for `background-image`.
+	 * @since 5.1.0 Added support for `text-transform`.
+	 * @since 5.2.0 Added support for `background-position` and `grid-template-columns`.
+	 * @since 5.3.0 Added support for `grid`, `flex` and `column` layout properties.
+	 *              Extend `background-*` support of individual properties.
+	 * @since 5.3.1 Added support for gradient backgrounds.
+	 * @since 5.7.1 Added support for `object-position`.
+	 * @since 5.8.0 Added support for `calc()` and `var()` values.
+	 *
+	 * @param string[] $attr Array of allowed CSS attributes.
+	 */
+	$allowed_attr = apply_filters(
+		'safe_style_css',
+		array(
+			'background',
+			'background-color',
+			'background-image',
+			'background-position',
+			'background-size',
+			'background-attachment',
+			'background-blend-mode',
 
-	if ( empty($allowed_attr) )
+			'border',
+			'border-radius',
+			'border-width',
+			'border-color',
+			'border-style',
+			'border-right',
+			'border-right-color',
+			'border-right-style',
+			'border-right-width',
+			'border-bottom',
+			'border-bottom-color',
+			'border-bottom-style',
+			'border-bottom-width',
+			'border-left',
+			'border-left-color',
+			'border-left-style',
+			'border-left-width',
+			'border-top',
+			'border-top-color',
+			'border-top-style',
+			'border-top-width',
+
+			'border-spacing',
+			'border-collapse',
+			'caption-side',
+
+			'columns',
+			'column-count',
+			'column-fill',
+			'column-gap',
+			'column-rule',
+			'column-span',
+			'column-width',
+
+			'color',
+			'font',
+			'font-family',
+			'font-size',
+			'font-style',
+			'font-variant',
+			'font-weight',
+			'letter-spacing',
+			'line-height',
+			'text-align',
+			'text-decoration',
+			'text-indent',
+			'text-transform',
+
+			'height',
+			'min-height',
+			'max-height',
+
+			'width',
+			'min-width',
+			'max-width',
+
+			'margin',
+			'margin-right',
+			'margin-bottom',
+			'margin-left',
+			'margin-top',
+
+			'padding',
+			'padding-right',
+			'padding-bottom',
+			'padding-left',
+			'padding-top',
+
+			'flex',
+			'flex-basis',
+			'flex-direction',
+			'flex-flow',
+			'flex-grow',
+			'flex-shrink',
+
+			'grid-template-columns',
+			'grid-auto-columns',
+			'grid-column-start',
+			'grid-column-end',
+			'grid-column-gap',
+			'grid-template-rows',
+			'grid-auto-rows',
+			'grid-row-start',
+			'grid-row-end',
+			'grid-row-gap',
+			'grid-gap',
+
+			'justify-content',
+			'justify-items',
+			'justify-self',
+			'align-content',
+			'align-items',
+			'align-self',
+
+			'clear',
+			'cursor',
+			'direction',
+			'float',
+			'list-style-type',
+			'object-position',
+			'overflow',
+			'vertical-align',
+		)
+	);
+
+	/*
+	 * CSS attributes that accept URL data types.
+	 *
+	 * This is in accordance to the CSS spec and unrelated to
+	 * the sub-set of supported attributes above.
+	 *
+	 * See: https://developer.mozilla.org/en-US/docs/Web/CSS/url
+	 */
+	$css_url_data_types = array(
+		'background',
+		'background-image',
+
+		'cursor',
+
+		'list-style',
+		'list-style-image',
+	);
+
+	/*
+	 * CSS attributes that accept gradient data types.
+	 *
+	 */
+	$css_gradient_data_types = array(
+		'background',
+		'background-image',
+	);
+
+	if ( empty( $allowed_attr ) ) {
 		return $css;
+	}
 
 	$css = '';
 	foreach ( $css_array as $css_item ) {
-		if ( $css_item == '' )
+		if ( '' === $css_item ) {
 			continue;
-		$css_item = trim( $css_item );
-		$found = false;
+		}
+
+		$css_item        = trim( $css_item );
+		$css_test_string = $css_item;
+		$found           = false;
+		$url_attr        = false;
+		$gradient_attr   = false;
+
 		if ( strpos( $css_item, ':' ) === false ) {
 			$found = true;
 		} else {
-			$parts = explode( ':', $css_item );
-			if ( in_array( trim( $parts[0] ), $allowed_attr ) )
-				$found = true;
+			$parts        = explode( ':', $css_item, 2 );
+			$css_selector = trim( $parts[0] );
+
+			if ( in_array( $css_selector, $allowed_attr, true ) ) {
+				$found         = true;
+				$url_attr      = in_array( $css_selector, $css_url_data_types, true );
+				$gradient_attr = in_array( $css_selector, $css_gradient_data_types, true );
+			}
 		}
+
+		if ( $found && $url_attr ) {
+			// Simplified: matches the sequence `url(*)`.
+			preg_match_all( '/url\([^)]+\)/', $parts[1], $url_matches );
+
+			foreach ( $url_matches[0] as $url_match ) {
+				// Clean up the URL from each of the matches above.
+				preg_match( '/^url\(\s*([\'\"]?)(.*)(\g1)\s*\)$/', $url_match, $url_pieces );
+
+				if ( empty( $url_pieces[2] ) ) {
+					$found = false;
+					break;
+				}
+
+				$url = trim( $url_pieces[2] );
+
+				if ( empty( $url ) || wp_kses_bad_protocol( $url, $allowed_protocols ) !== $url ) {
+					$found = false;
+					break;
+				} else {
+					// Remove the whole `url(*)` bit that was matched above from the CSS.
+					$css_test_string = str_replace( $url_match, '', $css_test_string );
+				}
+			}
+		}
+
+		if ( $found && $gradient_attr ) {
+			$css_value = trim( $parts[1] );
+			if ( preg_match( '/^(repeating-)?(linear|radial|conic)-gradient\(([^()]|rgb[a]?\([^()]*\))*\)$/', $css_value ) ) {
+				// Remove the whole `gradient` bit that was matched above from the CSS.
+				$css_test_string = str_replace( $css_value, '', $css_test_string );
+			}
+		}
+
 		if ( $found ) {
-			if( $css != '' )
-				$css .= ';';
-			$css .= $css_item;
+			// Allow CSS calc().
+			$css_test_string = preg_replace( '/calc\(((?:\([^()]*\)?|[^()])*)\)/', '', $css_test_string );
+			// Allow CSS var().
+			$css_test_string = preg_replace( '/\(?var\(--[a-zA-Z0-9_-]*\)/', '', $css_test_string );
+
+			// Check for any CSS containing \ ( & } = or comments,
+			// except for url(), calc(), or var() usage checked above.
+			$allow_css = ! preg_match( '%[\\\(&=}]|/\*%', $css_test_string );
+
+			/**
+			 * Filters the check for unsafe CSS in `safecss_filter_attr`.
+			 *
+			 * Enables developers to determine whether a section of CSS should be allowed or discarded.
+			 * By default, the value will be false if the part contains \ ( & } = or comments.
+			 * Return true to allow the CSS part to be included in the output.
+			 *
+			 * @since 5.5.0
+			 *
+			 * @param bool   $allow_css       Whether the CSS in the test string is considered safe.
+			 * @param string $css_test_string The CSS string to test.
+			 */
+			$allow_css = apply_filters( 'safecss_filter_attr_allow_css', $allow_css, $css_test_string );
+
+			 // Only add the CSS part if it passes the regex check.
+			if ( $allow_css ) {
+				if ( '' !== $css ) {
+					$css .= ';';
+				}
+
+				$css .= $css_item;
+			}
 		}
 	}
 
@@ -1201,27 +2427,38 @@ function safecss_filter_attr( $css, $deprecated = '' ) {
 }
 
 /**
- * Helper function to add global attributes to a tag in the allowed html list.
+ * Helper function to add global attributes to a tag in the allowed HTML list.
  *
  * @since 3.5.0
+ * @since 5.0.0 Add support for `data-*` wildcard attributes.
  * @access private
+ * @ignore
  *
  * @param array $value An array of attributes.
  * @return array The array of attributes with global attributes added.
  */
 function _wp_add_global_attributes( $value ) {
 	$global_attributes = array(
-		'class' => true,
-		'id' => true,
-		'style' => true,
-		'title' => true,
+		'aria-describedby' => true,
+		'aria-details'     => true,
+		'aria-label'       => true,
+		'aria-labelledby'  => true,
+		'aria-hidden'      => true,
+		'class'            => true,
+		'id'               => true,
+		'style'            => true,
+		'title'            => true,
+		'role'             => true,
+		'data-*'           => true,
 	);
 
-	if ( true === $value )
+	if ( true === $value ) {
 		$value = array();
+	}
 
-	if ( is_array( $value ) )
+	if ( is_array( $value ) ) {
 		return array_merge( $value, $global_attributes );
+	}
 
 	return $value;
 }