` or a comment ``.
	 *
	 * If the first character of the `$content` chunk _isn't_ one
	 * of these syntax elements, which always starts with `<`, then
	 * the match had to be for the final alternation of `>`. In such
	 * case, it's probably standing on its own and could be encoded
	 * with a character reference to remove ambiguity.
	 *
	 * In other words, if this chunk isn't from a match of a syntax
	 * token, it's just a plaintext greater-than (`>`) sign.
	 */
	if ( ! str_starts_with( $content, '<' ) ) {
		return '>';
	}
	/*
	 * When certain invalid syntax constructs appear, the HTML parser
	 * shifts into what's called the "bogus comment state." This is a
	 * plaintext state that consumes everything until the nearest `>`
	 * and then transforms the entire span into an HTML comment.
	 *
	 * Preserve these comments and do not treat them like tags.
	 *
	 * @see https://html.spec.whatwg.org/#bogus-comment-state
	 */
	if ( 1 === preg_match( '~^(?:[^a-zA-Z][^>]*>|]*>)$~', $content ) ) {
		/**
		 * Since the pattern matches `…>` and also ``, this will
		 * preserve the type of the cleaned-up token in the output.
		 */
		$opener  = $content[1];
		$content = substr( $content, 2, -1 );
		do {
			$prev    = $content;
			$content = wp_kses( $content, $allowed_html, $allowed_protocols );
		} while ( $prev !== $content );
		// Recombine the modified inner content with the original token structure.
		return "<{$opener}{$content}>";
	}
	/*
	 * Normative HTML comments should be handled separately as their
	 * parsing rules differ from those for tags and text nodes.
	 */
	if ( str_starts_with( $content, '' ), '', $content );
		while ( ( $newstring = wp_kses( $content, $allowed_html, $allowed_protocols ) ) !== $content ) {
			$content = $newstring;
		}
		if ( '' === $content ) {
			return '';
		}
		// Prevent multiple dashes in comments.
		$content = preg_replace( '/--+/', '-', $content );
		// Prevent three dashes closing a comment.
		$content = preg_replace( '/-$/', '', $content );
		return "";
	}
	// It's seriously malformed.
	if ( ! preg_match( '%^<\s*(/\s*)?([a-zA-Z0-9-]+)([^>]*)>?$%', $content, $matches ) ) {
		return '';
	}
	$slash    = trim( $matches[1] );
	$elem     = $matches[2];
	$attrlist = $matches[3];
	if ( ! is_array( $allowed_html ) ) {
		$allowed_html = wp_kses_allowed_html( $allowed_html );
	}
	// 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>";
	}
	return wp_kses_attr( $elem, $attrlist, $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 `wp_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.
 *
 * An array of allowed values can be defined for attributes. If the attribute value
 * doesn't fall into the list, the attribute will be removed from the tag.
 *
 * Attributes can be marked as required. If a required attribute is not present,
 * KSES will remove all attributes from the tag. As KSES doesn't match opening and
 * closing tags, it's not possible to safely remove the tag itself, the safest
 * fallback is to strip all attributes from the tag, instead.
 *
 * @since 1.0.0
 * @since 5.9.0 Added support for an array of allowed values for attributes.
 *              Added support for required attributes.
 *
 * @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 ) {
	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 ) ) {
		$xhtml_slash = ' /';
	}
	// 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 );
	// Check if there are attributes that are required.
	$required_attrs = array_filter(
		$allowed_html[ $element_low ],
		static function ( $required_attr_limits ) {
			return isset( $required_attr_limits['required'] ) && true === $required_attr_limits['required'];
		}
	);
	/*
	 * If a required attribute check fails, we can return nothing for a self-closing tag,
	 * but for a non-self-closing tag the best option is to return the element with attributes,
	 * as KSES doesn't handle matching the relevant closing tag.
	 */
	$stripped_tag = '';
	if ( empty( $xhtml_slash ) ) {
		$stripped_tag = "<$element>";
	}
	// Go through $attrarr, and save the allowed attributes for this element in $attr2.
	$attr2 = '';
	foreach ( $attrarr as $arreach ) {
		// Check if this attribute is required.
		$required = isset( $required_attrs[ strtolower( $arreach['name'] ) ] );
		if ( wp_kses_attr_check( $arreach['name'], $arreach['value'], $arreach['whole'], $arreach['vless'], $element, $allowed_html ) ) {
			$attr2 .= ' ' . $arreach['whole'];
			// If this was a required attribute, we can mark it as found.
			if ( $required ) {
				unset( $required_attrs[ strtolower( $arreach['name'] ) ] );
			}
		} elseif ( $required ) {
			// This attribute was required, but didn't pass the check. The entire tag is not allowed.
			return $stripped_tag;
		}
	}
	// If some required attributes weren't set, the entire tag is not allowed.
	if ( ! empty( $required_attrs ) ) {
		return $stripped_tag;
	}
	// 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 Added 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.
		 */
		if ( str_starts_with( $name_low, 'data-' ) && ! 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.
 *
 * This function does a lot of work. It parses an attribute list into an array
 * with attribute data, and tries to do the right thing even if it gets weird
 * input. It will add quotes around attribute values that don't have any quotes
 * 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'`).
 *
 * @since 1.0.0
 *
 * @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;
	$attrname = '';
	$uris     = wp_kses_uri_attributes();
	// Loop through the whole attribute list.
	while ( strlen( $attr ) !== 0 ) {
		$working = 0; // Was the last operation successful?
		switch ( $mode ) {
			case 0:
				if ( preg_match( '/^([_a-zA-Z][-_a-zA-Z0-9:.]*)/', $attr, $match ) ) {
					$attrname = $match[1];
					$working  = 1;
					$mode     = 1;
					$attr     = preg_replace( '/^[_a-zA-Z][-_a-zA-Z0-9:.]*/', '', $attr );
				}
				break;
			case 1:
				if ( preg_match( '/^\s*=\s*/', $attr ) ) { // Equals sign.
					$working = 1;
					$mode    = 2;
					$attr    = preg_replace( '/^\s*=\s*/', '', $attr );
					break;
				}
				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',
						);
					}
					$attr = preg_replace( '/^\s+/', '', $attr );
				}
				break;
			case 2:
				if ( preg_match( '%^"([^"]*)"(\s+|/?$)%', $attr, $match ) ) {
					// "value"
					$thisval = $match[1];
					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',
						);
					}
					$working = 1;
					$mode    = 0;
					$attr    = preg_replace( '/^"[^"]*"(\s+|$)/', '', $attr );
					break;
				}
				if ( preg_match( "%^'([^']*)'(\s+|/?$)%", $attr, $match ) ) {
					// 'value'
					$thisval = $match[1];
					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',
						);
					}
					$working = 1;
					$mode    = 0;
					$attr    = preg_replace( "/^'[^']*'(\s+|$)/", '', $attr );
					break;
				}
				if ( preg_match( "%^([^\s\"']+)(\s+|/?$)%", $attr, $match ) ) {
					// value
					$thisval = $match[1];
					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',
						);
					}
					// We add quotes to conform to W3C's HTML spec.
					$working = 1;
					$mode    = 0;
					$attr    = preg_replace( "%^[^\s\"']+(\s+|$)%", '', $attr );
				}
				break;
		} // End switch.
		if ( 0 === $working ) { // Not well-formed, remove and try again.
			$attr = wp_kses_html_error( $attr );
			$mode = 0;
		}
	} // End while.
	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();
	}
	$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.
		';
	/*
	 * Although it is possible to reduce this procedure to a single regexp,
	 * we must run that regexp twice to get exactly the expected result.
	 *
	 * Note: do NOT remove the `x` modifiers as they are essential for the above regex!
	 */
	$validation = "/^($regex)+$/x";
	$extraction = "/$regex/x";
	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",
 * and "valueless".
 *
 * @since 1.0.0
 *
 * @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 ) {
	$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.
			 */
			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.
			 */
			if ( strlen( $value ) < $checkvalue ) {
				$ok = false;
			}
			break;
		case 'maxval':
			/*
			 * The maxval check does two things: it checks that the attribute value is
			 * an integer from 0 and up, without an excessive amount of zeroes or
			 * whitespace (to avoid Buffer Overflows). It also checks that the attribute
			 * value is not greater than the given value.
			 * This check can be used to avoid Denial of Service attacks.
			 */
			if ( ! preg_match( '/^\s{0,6}[0-9]{1,6}\s{0,6}$/', $value ) ) {
				$ok = false;
			}
			if ( $value > $checkvalue ) {
				$ok = false;
			}
			break;
		case 'minval':
			/*
			 * The minval check makes sure that the attribute value is a positive integer,
			 * and that it is not smaller than the given value.
			 */
			if ( ! preg_match( '/^\s{0,6}[0-9]{1,6}\s{0,6}$/', $value ) ) {
				$ok = false;
			}
			if ( $value < $checkvalue ) {
				$ok = false;
			}
			break;
		case 'valueless':
			/*
			 * The valueless check makes sure if the attribute has a value
			 * (like `
`) or not (`