'textLength';

				case 'viewbox':
					return 'viewBox';

				case 'viewtarget':
					return 'viewTarget';

				case 'xchannelselector':
					return 'xChannelSelector';

				case 'ychannelselector':
					return 'yChannelSelector';

				case 'zoomandpan':
					return 'zoomAndPan';
			}
		}

		if ( 'html' !== $namespace ) {
			switch ( $lower_name ) {
				case 'xlink:actuate':
					return 'xlink actuate';

				case 'xlink:arcrole':
					return 'xlink arcrole';

				case 'xlink:href':
					return 'xlink href';

				case 'xlink:role':
					return 'xlink role';

				case 'xlink:show':
					return 'xlink show';

				case 'xlink:title':
					return 'xlink title';

				case 'xlink:type':
					return 'xlink type';

				case 'xml:lang':
					return 'xml lang';

				case 'xml:space':
					return 'xml space';

				case 'xmlns':
					return 'xmlns';

				case 'xmlns:xlink':
					return 'xmlns xlink';
			}
		}

		return $attribute_name;
	}

	/**
	 * Indicates if the currently matched tag contains the self-closing flag.
	 *
	 * No HTML elements ought to have the self-closing flag and for those, the self-closing
	 * flag will be ignored. For void elements this is benign because they "self close"
	 * automatically. For non-void HTML elements though problems will appear if someone
	 * intends to use a self-closing element in place of that element with an empty body.
	 * For HTML foreign elements and custom elements the self-closing flag determines if
	 * they self-close or not.
	 *
	 * This function does not determine if a tag is self-closing,
	 * but only if the self-closing flag is present in the syntax.
	 *
	 * @since 6.3.0
	 *
	 * @return bool Whether the currently matched tag contains the self-closing flag.
	 */
	public function has_self_closing_flag(): bool {
		if ( self::STATE_MATCHED_TAG !== $this->parser_state ) {
			return false;
		}

		/*
		 * The self-closing flag is the solidus at the _end_ of the tag, not the beginning.
		 *
		 * Example:
		 *
		 *     <figure />
		 *             ^ this appears one character before the end of the closing ">".
		 */
		return '/' === $this->html[ $this->token_starts_at + $this->token_length - 2 ];
	}

	/**
	 * Indicates if the current tag token is a tag closer.
	 *
	 * Example:
	 *
	 *     $p = new WP_HTML_Tag_Processor( '<div></div>' );
	 *     $p->next_tag( array( 'tag_name' => 'div', 'tag_closers' => 'visit' ) );
	 *     $p->is_tag_closer() === false;
	 *
	 *     $p->next_tag( array( 'tag_name' => 'div', 'tag_closers' => 'visit' ) );
	 *     $p->is_tag_closer() === true;
	 *
	 * @since 6.2.0
	 * @since 6.7.0 Reports all BR tags as opening tags.
	 *
	 * @return bool Whether the current tag is a tag closer.
	 */
	public function is_tag_closer(): bool {
		return (
			self::STATE_MATCHED_TAG === $this->parser_state &&
			$this->is_closing_tag &&

			/*
			 * The BR tag can only exist as an opening tag. If something like `</br>`
			 * appears then the HTML parser will treat it as an opening tag with no
			 * attributes. The BR tag is unique in this way.
			 *
			 * @see https://html.spec.whatwg.org/#parsing-main-inbody
			 */
			'BR' !== $this->get_tag()
		);
	}

	/**
	 * Indicates the kind of matched token, if any.
	 *
	 * This differs from `get_token_name()` in that it always
	 * returns a static string indicating the type, whereas
	 * `get_token_name()` may return values derived from the
	 * token itself, such as a tag name or processing
	 * instruction tag.
	 *
	 * Possible values:
	 *  - `#tag` when matched on a tag.
	 *  - `#text` when matched on a text node.
	 *  - `#cdata-section` when matched on a CDATA node.
	 *  - `#comment` when matched on a comment.
	 *  - `#doctype` when matched on a DOCTYPE declaration.
	 *  - `#presumptuous-tag` when matched on an empty tag closer.
	 *  - `#funky-comment` when matched on a funky comment.
	 *
	 * @since 6.5.0
	 *
	 * @return string|null What kind of token is matched, or null.
	 */
	public function get_token_type(): ?string {
		switch ( $this->parser_state ) {
			case self::STATE_MATCHED_TAG:
				return '#tag';

			case self::STATE_DOCTYPE:
				return '#doctype';

			default:
				return $this->get_token_name();
		}
	}

	/**
	 * Returns the node name represented by the token.
	 *
	 * This matches the DOM API value `nodeName`. Some values
	 * are static, such as `#text` for a text node, while others
	 * are dynamically generated from the token itself.
	 *
	 * Dynamic names:
	 *  - Uppercase tag name for tag matches.
	 *  - `html` for DOCTYPE declarations.
	 *
	 * Note that if the Tag Processor is not matched on a token
	 * then this function will return `null`, either because it
	 * hasn't yet found a token or because it reached the end
	 * of the document without matching a token.
	 *
	 * @since 6.5.0
	 *
	 * @return string|null Name of the matched token.
	 */
	public function get_token_name(): ?string {
		switch ( $this->parser_state ) {
			case self::STATE_MATCHED_TAG:
				return $this->get_tag();

			case self::STATE_TEXT_NODE:
				return '#text';

			case self::STATE_CDATA_NODE:
				return '#cdata-section';

			case self::STATE_COMMENT:
				return '#comment';

			case self::STATE_DOCTYPE:
				return 'html';

			case self::STATE_PRESUMPTUOUS_TAG:
				return '#presumptuous-tag';

			case self::STATE_FUNKY_COMMENT:
				return '#funky-comment';
		}

		return null;
	}

	/**
	 * Indicates what kind of comment produced the comment node.
	 *
	 * Because there are different kinds of HTML syntax which produce
	 * comments, the Tag Processor tracks and exposes this as a type
	 * for the comment. Nominally only regular HTML comments exist as
	 * they are commonly known, but a number of unrelated syntax errors
	 * also produce comments.
	 *
	 * @see self::COMMENT_AS_ABRUPTLY_CLOSED_COMMENT
	 * @see self::COMMENT_AS_CDATA_LOOKALIKE
	 * @see self::COMMENT_AS_INVALID_HTML
	 * @see self::COMMENT_AS_HTML_COMMENT
	 * @see self::COMMENT_AS_PI_NODE_LOOKALIKE
	 *
	 * @since 6.5.0
	 *
	 * @return string|null
	 */
	public function get_comment_type(): ?string {
		if ( self::STATE_COMMENT !== $this->parser_state ) {
			return null;
		}

		return $this->comment_type;
	}

	/**
	 * Returns the text of a matched comment or null if not on a comment type node.
	 *
	 * This method returns the entire text content of a comment node as it
	 * would appear in the browser.
	 *
	 * This differs from {@see ::get_modifiable_text()} in that certain comment
	 * types in the HTML API cannot allow their entire comment text content to
	 * be modified. Namely, "bogus comments" of the form `<?not allowed in html>`
	 * will create a comment whose text content starts with `?`. Note that if
	 * that character were modified, it would be possible to change the node
	 * type.
	 *
	 * @since 6.7.0
	 *
	 * @return string|null The comment text as it would appear in the browser or null
	 *                     if not on a comment type node.
	 */
	public function get_full_comment_text(): ?string {
		if ( self::STATE_FUNKY_COMMENT === $this->parser_state ) {
			return $this->get_modifiable_text();
		}

		if ( self::STATE_COMMENT !== $this->parser_state ) {
			return null;
		}

		switch ( $this->get_comment_type() ) {
			case self::COMMENT_AS_HTML_COMMENT:
			case self::COMMENT_AS_ABRUPTLY_CLOSED_COMMENT:
				return $this->get_modifiable_text();

			case self::COMMENT_AS_CDATA_LOOKALIKE:
				return "[CDATA[{$this->get_modifiable_text()}]]";

			case self::COMMENT_AS_PI_NODE_LOOKALIKE:
				return "?{$this->get_tag()}{$this->get_modifiable_text()}?";

			/*
			 * This represents "bogus comments state" from HTML tokenization.
			 * This can be entered by `<?` or `<!`, where `?` is included in
			 * the comment text but `!` is not.
			 */
			case self::COMMENT_AS_INVALID_HTML:
				$preceding_character = $this->html[ $this->text_starts_at - 1 ];
				$comment_start       = '?' === $preceding_character ? '?' : '';
				return "{$comment_start}{$this->get_modifiable_text()}";
		}

		return null;
	}

	/**
	 * Subdivides a matched text node, splitting NULL byte sequences and decoded whitespace as
	 * distinct nodes prefixes.
	 *
	 * Note that once anything that's neither a NULL byte nor decoded whitespace is
	 * encountered, then the remainder of the text node is left intact as generic text.
	 *
	 *  - The HTML Processor uses this to apply distinct rules for different kinds of text.
	 *  - Inter-element whitespace can be detected and skipped with this method.
	 *
	 * Text nodes aren't eagerly subdivided because there's no need to split them unless
	 * decisions are being made on NULL byte sequences or whitespace-only text.
	 *
	 * Example:
	 *
	 *     $processor = new WP_HTML_Tag_Processor( "\x00Apples & Oranges" );
	 *     true  === $processor->next_token();                   // Text is "Apples & Oranges".
	 *     true  === $processor->subdivide_text_appropriately(); // Text is "".
	 *     true  === $processor->next_token();                   // Text is "Apples & Oranges".
	 *     false === $processor->subdivide_text_appropriately();
	 *
	 *     $processor = new WP_HTML_Tag_Processor( "&#x13; \r\n\tMore" );
	 *     true  === $processor->next_token();                   // Text is "␤ ␤␉More".
	 *     true  === $processor->subdivide_text_appropriately(); // Text is "␤ ␤␉".
	 *     true  === $processor->next_token();                   // Text is "More".
	 *     false === $processor->subdivide_text_appropriately();
	 *
	 * @since 6.7.0
	 *
	 * @return bool Whether the text node was subdivided.
	 */
	public function subdivide_text_appropriately(): bool {
		if ( self::STATE_TEXT_NODE !== $this->parser_state ) {
			return false;
		}

		$this->text_node_classification = self::TEXT_IS_GENERIC;

		/*
		 * NULL bytes are treated categorically different than numeric character
		 * references whose number is zero. `&#x00;` is not the same as `"\x00"`.
		 */
		$leading_nulls = strspn( $this->html, "\x00", $this->text_starts_at, $this->text_length );
		if ( $leading_nulls > 0 ) {
			$this->token_length             = $leading_nulls;
			$this->text_length              = $leading_nulls;
			$this->bytes_already_parsed     = $this->token_starts_at + $leading_nulls;
			$this->text_node_classification = self::TEXT_IS_NULL_SEQUENCE;
			return true;
		}

		/*
		 * Start a decoding loop to determine the point at which the
		 * text subdivides. This entails raw whitespace bytes and any
		 * character reference that decodes to the same.
		 */
		$at  = $this->text_starts_at;
		$end = $this->text_starts_at + $this->text_length;
		while ( $at < $end ) {
			$skipped = strspn( $this->html, " \t\f\r\n", $at, $end - $at );
			$at     += $skipped;

			if ( $at < $end && '&' === $this->html[ $at ] ) {
				$matched_byte_length = null;
				$replacement         = WP_HTML_Decoder::read_character_reference( 'data', $this->html, $at, $matched_byte_length );
				if ( isset( $replacement ) && 1 === strspn( $replacement, " \t\f\r\n" ) ) {
					$at += $matched_byte_length;
					continue;
				}
			}

			break;
		}

		if ( $at > $this->text_starts_at ) {
			$new_length                     = $at - $this->text_starts_at;
			$this->text_length              = $new_length;
			$this->token_length             = $new_length;
			$this->bytes_already_parsed     = $at;
			$this->text_node_classification = self::TEXT_IS_WHITESPACE;
			return true;
		}

		return false;
	}

	/**
	 * Returns the modifiable text for a matched token, or an empty string.
	 *
	 * Modifiable text is text content that may be read and changed without
	 * changing the HTML structure of the document around it. This includes
	 * the contents of `#text` nodes in the HTML as well as the inner
	 * contents of HTML comments, Processing Instructions, and others, even
	 * though these nodes aren't part of a parsed DOM tree. They also contain
	 * the contents of SCRIPT and STYLE tags, of TEXTAREA tags, and of any
	 * other section in an HTML document which cannot contain HTML markup (DATA).
	 *
	 * If a token has no modifiable text then an empty string is returned to
	 * avoid needless crashing or type errors. An empty string does not mean
	 * that a token has modifiable text, and a token with modifiable text may
	 * have an empty string (e.g. a comment with no contents).
	 *
	 * Limitations:
	 *
	 *  - This function will not strip the leading newline appropriately
	 *    after seeking into a LISTING or PRE element. To ensure that the
	 *    newline is treated properly, seek to the LISTING or PRE opening
	 *    tag instead of to the first text node inside the element.
	 *
	 * @since 6.5.0
	 * @since 6.7.0 Replaces NULL bytes (U+0000) and newlines appropriately.
	 *
	 * @return string
	 */
	public function get_modifiable_text(): string {
		$has_enqueued_update = isset( $this->lexical_updates['modifiable text'] );

		if ( ! $has_enqueued_update && ( null === $this->text_starts_at || 0 === $this->text_length ) ) {
			return '';
		}

		$text = $has_enqueued_update
			? $this->lexical_updates['modifiable text']->text
			: substr( $this->html, $this->text_starts_at, $this->text_length );

		/*
		 * Pre-processing the input stream would normally happen before
		 * any parsing is done, but deferring it means it's possible to
		 * skip in most cases. When getting the modifiable text, however
		 * it's important to apply the pre-processing steps, which is
		 * normalizing newlines.
		 *
		 * @see https://html.spec.whatwg.org/#preprocessing-the-input-stream
		 * @see https://infra.spec.whatwg.org/#normalize-newlines
		 */
		$text = str_replace( "\r\n", "\n", $text );
		$text = str_replace( "\r", "\n", $text );

		// Comment data is not decoded.
		if (
			self::STATE_CDATA_NODE === $this->parser_state ||
			self::STATE_COMMENT === $this->parser_state ||
			self::STATE_DOCTYPE === $this->parser_state ||
			self::STATE_FUNKY_COMMENT === $this->parser_state
		) {
			return str_replace( "\x00", "\u{FFFD}", $text );
		}

		$tag_name = $this->get_token_name();
		if (
			// Script data is not decoded.
			'SCRIPT' === $tag_name ||

			// RAWTEXT data is not decoded.
			'IFRAME' === $tag_name ||
			'NOEMBED' === $tag_name ||
			'NOFRAMES' === $tag_name ||
			'STYLE' === $tag_name ||
			'XMP' === $tag_name
		) {
			return str_replace( "\x00", "\u{FFFD}", $text );
		}

		$decoded = WP_HTML_Decoder::decode_text_node( $text );

		/*
		 * Skip the first line feed after LISTING, PRE, and TEXTAREA opening tags.
		 *
		 * Note that this first newline may come in the form of a character
		 * reference, such as `&#x0a;`, and so it's important to perform
		 * this transformation only after decoding the raw text content.
		 */
		if (
			( "\n" === ( $decoded[0] ?? '' ) ) &&
			( ( $this->skip_newline_at === $this->token_starts_at && '#text' === $tag_name ) || 'TEXTAREA' === $tag_name )
		) {
			$decoded = substr( $decoded, 1 );
		}

		/*
		 * Only in normative text nodes does the NULL byte (U+0000) get removed.
		 * In all other contexts it's replaced by the replacement character (U+FFFD)
		 * for security reasons (to avoid joining together strings that were safe
		 * when separated, but not when joined).
		 *
		 * @todo Inside HTML integration points and MathML integration points, the
		 *       text is processed according to the insertion mode, not according
		 *       to the foreign content rules. This should strip the NULL bytes.
		 */
		return ( '#text' === $tag_name && 'html' === $this->get_namespace() )
			? str_replace( "\x00", '', $decoded )
			: str_replace( "\x00", "\u{FFFD}", $decoded );
	}

	/**
	 * Sets the modifiable text for the matched token, if matched.
	 *
	 * Modifiable text is text content that may be read and changed without
	 * changing the HTML structure of the document around it. This includes
	 * the contents of `#text` nodes in the HTML as well as the inner
	 * contents of HTML comments, Processing Instructions, and others, even
	 * though these nodes aren't part of a parsed DOM tree. They also contain
	 * the contents of SCRIPT and STYLE tags, of TEXTAREA tags, and of any
	 * other section in an HTML document which cannot contain HTML markup (DATA).
	 *
	 * Not all modifiable text may be set by this method, and not all content
	 * may be set as modifiable text. In the case that this fails it will return
	 * `false` indicating as much. For instance, it will not allow inserting the
	 * string `</script` into a SCRIPT element, because the rules for escaping
	 * that safely are complicated. Similarly, it will not allow setting content
	 * into a comment which would prematurely terminate the comment.
	 *
	 * Example:
	 *
	 *     // Add a preface to all STYLE contents.
	 *     while ( $processor->next_tag( 'STYLE' ) ) {
	 *         $style = $processor->get_modifiable_text();
	 *         $processor->set_modifiable_text( "// Made with love on the World Wide Web\n{$style}" );
	 *     }
	 *
	 *     // Replace smiley text with Emoji smilies.
	 *     while ( $processor->next_token() ) {
	 *         if ( '#text' !== $processor->get_token_name() ) {
	 *             continue;
	 *         }
	 *
	 *         $chunk = $processor->get_modifiable_text();
	 *         if ( ! str_contains( $chunk, ':)' ) ) {
	 *             continue;
	 *         }
	 *
	 *         $processor->set_modifiable_text( str_replace( ':)', '🙂', $chunk ) );
	 *     }
	 *
	 * This function handles all necessary HTML encoding. Provide normal, unescaped string values.
	 * The HTML API will encode the strings appropriately so that the browser will interpret them
	 * as the intended value.
	 *
	 * Example:
	 *
	 *     // Renders as “Eggs & Milk” in a browser, encoded as `<p>Eggs &amp; Milk</p>`.
	 *     $processor->set_modifiable_text( 'Eggs & Milk' );
	 *
	 *     // Renders as “Eggs &amp; Milk” in a browser, encoded as `<p>Eggs &amp;amp; Milk</p>`.
	 *     $processor->set_modifiable_text( 'Eggs &amp; Milk' );
	 *
	 * @since 6.7.0
	 * @since 6.9.0 Escapes all character references instead of trying to avoid double-escaping.
	 *
	 * @param string $plaintext_content New text content to represent in the matched token.
	 * @return bool Whether the text was able to update.
	 */
	public function set_modifiable_text( string $plaintext_content ): bool {
		if ( self::STATE_TEXT_NODE === $this->parser_state ) {
			$this->lexical_updates['modifiable text'] = new WP_HTML_Text_Replacement(
				$this->text_starts_at,
				$this->text_length,
				strtr(
					$plaintext_content,
					array(
						'<' => '&lt;',
						'>' => '&gt;',
						'&' => '&amp;',
						'"' => '&quot;',
						"'" => '&apos;',
					)
				)
			);

			return true;
		}

		// Comment data is not encoded.
		if (
			self::STATE_COMMENT === $this->parser_state &&
			self::COMMENT_AS_HTML_COMMENT === $this->comment_type
		) {
			// Check if the text could close the comment.
			if ( 1 === preg_match( '/--!?>/', $plaintext_content ) ) {
				return false;
			}

			$this->lexical_updates['modifiable text'] = new WP_HTML_Text_Replacement(
				$this->text_starts_at,
				$this->text_length,
				$plaintext_content
			);

			return true;
		}

		if ( self::STATE_MATCHED_TAG !== $this->parser_state ) {
			return false;
		}

		switch ( $this->get_tag() ) {
			case 'SCRIPT':
				/**
				 * This is over-protective, but ensures the update doesn't break
				 * the HTML structure of the SCRIPT element.
				 *
				 * More thorough analysis could track the HTML tokenizer states
				 * and to ensure that the SCRIPT element closes at the expected
				 * SCRIPT close tag as is done in {@see ::skip_script_data()}.
				 *
				 * A SCRIPT element could be closed prematurely by contents
				 * like `</script>`. A SCRIPT element could be prevented from
				 * closing by contents like `<!--<script>`.
				 *
				 * The following strings are essential for dangerous content,
				 * although they are insufficient on their own. This trade-off
				 * prevents dangerous scripts from being sent to the browser.
				 * It is also unlikely to produce HTML that may confuse more
				 * basic HTML tooling.
				 */
				if (
					false !== stripos( $plaintext_content, '</script' ) ||
					false !== stripos( $plaintext_content, '<script' )
				) {
					return false;
				}

				$this->lexical_updates['modifiable text'] = new WP_HTML_Text_Replacement(
					$this->text_starts_at,
					$this->text_length,
					$plaintext_content
				);

				return true;

			case 'STYLE':
				$plaintext_content = preg_replace_callback(
					'~</(?P<TAG_NAME>style)~i',
					static function ( $tag_match ) {
						return "\\3c\\2f{$tag_match['TAG_NAME']}";
					},
					$plaintext_content
				);

				$this->lexical_updates['modifiable text'] = new WP_HTML_Text_Replacement(
					$this->text_starts_at,
					$this->text_length,
					$plaintext_content
				);

				return true;

			case 'TEXTAREA':
			case 'TITLE':
				$plaintext_content = preg_replace_callback(
					"~</(?P<TAG_NAME>{$this->get_tag()})~i",
					static function ( $tag_match ) {
						return "&lt;/{$tag_match['TAG_NAME']}";
					},
					$plaintext_content
				);

				/*
				 * These don't _need_ to be escaped, but since they are decoded it's
				 * safe to leave them escaped and this can prevent other code from
				 * naively detecting tags within the contents.
				 *
				 * @todo It would be useful to prefix a multiline replacement text
				 *       with a newline, but not necessary. This is for aesthetics.
				 */
				$this->lexical_updates['modifiable text'] = new WP_HTML_Text_Replacement(
					$this->text_starts_at,
					$this->text_length,
					$plaintext_content
				);

				return true;
		}

		return false;
	}

	/**
	 * Updates or creates a new attribute on the currently matched tag with the passed value.
	 *
	 * This function handles all necessary HTML encoding. Provide normal, unescaped string values.
	 * The HTML API will encode the strings appropriately so that the browser will interpret them
	 * as the intended value.
	 *
	 * Example:
	 *
	 *     // Renders “Eggs & Milk” in a browser, encoded as `<abbr title="Eggs &amp; Milk">`.
	 *     $processor->set_attribute( 'title', 'Eggs & Milk' );
	 *
	 *     // Renders “Eggs &amp; Milk” in a browser, encoded as `<abbr title="Eggs &amp;amp; Milk">`.
	 *     $processor->set_attribute( 'title', 'Eggs &amp; Milk' );
	 *
	 *     // Renders `true` as `<abbr title>`.
	 *     $processor->set_attribute( 'title', true );
	 *
	 *     // Renders without the attribute for `false` as `<abbr>`.
	 *     $processor->set_attribute( 'title', false );
	 *
	 * Special handling is provided for boolean attribute values:
	 *  - When `true` is passed as the value, then only the attribute name is added to the tag.
	 *  - When `false` is passed, the attribute gets removed if it existed before.
	 *
	 * @since 6.2.0
	 * @since 6.2.1 Fix: Only create a single update for multiple calls with case-variant attribute names.
	 * @since 6.9.0 Escapes all character references instead of trying to avoid double-escaping.
	 *
	 * @param string      $name  The attribute name to target.
	 * @param string|bool $value The new attribute value.
	 * @return bool Whether an attribute value was set.
	 */
	public function set_attribute( $name, $value ): bool {
		if (
			self::STATE_MATCHED_TAG !== $this->parser_state ||
			$this->is_closing_tag
		) {
			return false;
		}

		$name_length = strlen( $name );

		/**
		 * WordPress rejects more characters than are strictly forbidden
		 * in HTML5. This is to prevent additional security risks deeper
		 * in the WordPress and plugin stack. Specifically the following
		 * are not allowed to be set as part of an HTML attribute name:
		 *
		 *  - greater-than “>”
		 *  - ampersand “&”
		 *
		 * @see https://html.spec.whatwg.org/#attributes-2
		 */
		if (
			0 === $name_length ||
			// Syntax-like characters.
			strcspn( $name, '"\'>&</ =' ) !== $name_length ||
			// Control characters.
			strcspn(
				$name,
				"\x00\x01\x02\x03\x04\x05\x06\x07\x08\x09\x0A\x0B\x0C\x0D\x0E\x0F" .
				"\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1A\x1B\x1C\x1D\x1E\x1F"
			) !== $name_length ||
			// Unicode noncharacters.
			wp_has_noncharacters( $name )
		) {
			_doing_it_wrong(
				__METHOD__,
				__( 'Invalid attribute name.' ),
				'6.2.0'
			);

			return false;
		}

		/*
		 * > The values "true" and "false" are not allowed on boolean attributes.
		 * > To represent a false value, the attribute has to be omitted altogether.
		 *     - HTML5 spec, https://html.spec.whatwg.org/#boolean-attributes
		 */
		if ( false === $value ) {
			return $this->remove_attribute( $name );
		}

		if ( true === $value ) {
			$updated_attribute = $name;
		} else {
			$comparable_name = strtolower( $name );

			/**
			 * Escape attribute values appropriately.
			 *
			 * @see https://html.spec.whatwg.org/#attributes-3
			 */
			$escaped_new_value = in_array( $comparable_name, wp_kses_uri_attributes(), true )
				? esc_url( $value )
				: strtr(
					$value,
					array(
						'<' => '&lt;',
						'>' => '&gt;',
						'&' => '&amp;',
						'"' => '&quot;',
						"'" => '&apos;',
					)
				);

			// If the escaping functions wiped out the update, reject it and indicate it was rejected.
			if ( '' === $escaped_new_value && '' !== $value ) {
				return false;
			}

			$updated_attribute = "{$name}=\"{$escaped_new_value}\"";
		}

		/*
		 * > There must never be two or more attributes on
		 * > the same start tag whose names are an ASCII
		 * > case-insensitive match for each other.
		 *     - HTML 5 spec
		 *
		 * @see https://html.spec.whatwg.org/multipage/syntax.html#attributes-2:ascii-case-insensitive
		 */
		$comparable_name = strtolower( $name );

		if ( isset( $this->attributes[ $comparable_name ] ) ) {
			/*
			 * Update an existing attribute.
			 *
			 * Example – set attribute id to "new" in <div id="initial_id" />:
			 *
			 *     <div id="initial_id"/>
			 *          ^-------------^
			 *          start         end
			 *     replacement: `id="new"`
			 *
			 *     Result: <div id="new"/>
			 */
			$existing_attribute                        = $this->attributes[ $comparable_name ];
			$this->lexical_updates[ $comparable_name ] = new WP_HTML_Text_Replacement(
				$existing_attribute->start,
				$existing_attribute->length,
				$updated_attribute
			);
		} else {
			/*
			 * Create a new attribute at the tag's name end.
			 *
			 * Example – add attribute id="new" to <div />:
			 *
			 *     <div/>
			 *         ^
			 *         start and end
			 *     replacement: ` id="new"`
			 *
			 *     Result: <div id="new"/>
			 */
			$this->lexical_updates[ $comparable_name ] = new WP_HTML_Text_Replacement(
				$this->tag_name_starts_at + $this->tag_name_length,
				0,
				' ' . $updated_attribute
			);
		}

		/*
		 * Any calls to update the `class` attribute directly should wipe out any
		 * enqueued class changes from `add_class` and `remove_class`.
		 */
		if ( 'class' === $comparable_name && ! empty( $this->classname_updates ) ) {
			$this->classname_updates = array();
		}

		return true;
	}

	/**
	 * Remove an attribute from the currently-matched tag.
	 *
	 * @since 6.2.0
	 *
	 * @param string $name The attribute name to remove.
	 * @return bool Whether an attribute was removed.
	 */
	public function remove_attribute( $name ): bool {
		if (
			self::STATE_MATCHED_TAG !== $this->parser_state ||
			$this->is_closing_tag
		) {
			return false;
		}

		/*
		 * > There must never be two or more attributes on
		 * > the same start tag whose names are an ASCII
		 * > case-insensitive match for each other.
		 *     - HTML 5 spec
		 *
		 * @see https://html.spec.whatwg.org/multipage/syntax.html#attributes-2:ascii-case-insensitive
		 */
		$name = strtolower( $name );

		/*
		 * Any calls to update the `class` attribute directly should wipe out any
		 * enqueued class changes from `add_class` and `remove_class`.
		 */
		if ( 'class' === $name && count( $this->classname_updates ) !== 0 ) {
			$this->classname_updates = array();
		}

		/*
		 * If updating an attribute that didn't exist in the input
		 * document, then remove the enqueued update and move on.
		 *
		 * For example, this might occur when calling `remove_attribute()`
		 * after calling `set_attribute()` for the same attribute
		 * and when that attribute wasn't originally present.
		 */
		if ( ! isset( $this->attributes[ $name ] ) ) {
			if ( isset( $this->lexical_updates[ $name ] ) ) {
				unset( $this->lexical_updates[ $name ] );
			}
			return false;
		}

		/*
		 * Removes an existing tag attribute.
		 *
		 * Example – remove the attribute id from <div id="main"/>:
		 *    <div id="initial_id"/>
		 *         ^-------------^
		 *         start         end
		 *    replacement: ``
		 *
		 *    Result: <div />
		 */
		$this->lexical_updates[ $name ] = new WP_HTML_Text_Replacement(
			$this->attributes[ $name ]->start,
			$this->attributes[ $name ]->length,
			''
		);

		// Removes any duplicated attributes if they were also present.
		foreach ( $this->duplicate_attributes[ $name ] ?? array() as $attribute_token ) {
			$this->lexical_updates[] = new WP_HTML_Text_Replacement(
				$attribute_token->start,
				$attribute_token->length,
				''
			);
		}

		return true;
	}

	/**
	 * Adds a new class name to the currently matched tag.
	 *
	 * @since 6.2.0
	 *
	 * @param string $class_name The class name to add.
	 * @return bool Whether the class was set to be added.
	 */
	public function add_class( $class_name ): bool {
		if (
			self::STATE_MATCHED_TAG !== $this->parser_state ||
			$this->is_closing_tag
		) {
			return false;
		}

		if ( self::QUIRKS_MODE !== $this->compat_mode ) {
			$this->classname_updates[ $class_name ] = self::ADD_CLASS;
			return true;
		}

		/*
		 * Because class names are matched ASCII-case-insensitively in quirks mode,
		 * this needs to see if a case variant of the given class name is already
		 * enqueued and update that existing entry, if so. This picks the casing of
		 * the first-provided class name for all lexical variations.
		 */
		$class_name_length = strlen( $class_name );
		foreach ( $this->classname_updates as $updated_name => $action ) {
			if (
				strlen( $updated_name ) === $class_name_length &&
				0 === substr_compare( $updated_name, $class_name, 0, $class_name_length, true )
			) {
				$this->classname_updates[ $updated_name ] = self::ADD_CLASS;
				return true;
			}
		}

		$this->classname_updates[ $class_name ] = self::ADD_CLASS;
		return true;
	}

	/**
	 * Removes a class name from the currently matched tag.
	 *
	 * @since 6.2.0
	 *
	 * @param string $class_name The class name to remove.
	 * @return bool Whether the class was set to be removed.
	 */
	public function remove_class( $class_name ): bool {
		if (
			self::STATE_MATCHED_TAG !== $this->parser_state ||
			$this->is_closing_tag
		) {
			return false;
		}

		if ( self::QUIRKS_MODE !== $this->compat_mode ) {
			$this->classname_updates[ $class_name ] = self::REMOVE_CLASS;
			return true;
		}

		/*
		 * Because class names are matched ASCII-case-insensitively in quirks mode,
		 * this needs to see if a case variant of the given class name is already
		 * enqueued and update that existing entry, if so. This picks the casing of
		 * the first-provided class name for all lexical variations.
		 */
		$class_name_length = strlen( $class_name );
		foreach ( $this->classname_updates as $updated_name => $action ) {
			if (
				strlen( $updated_name ) === $class_name_length &&
				0 === substr_compare( $updated_name, $class_name, 0, $class_name_length, true )
			) {
				$this->classname_updates[ $updated_name ] = self::REMOVE_CLASS;
				return true;
			}
		}

		$this->classname_updates[ $class_name ] = self::REMOVE_CLASS;
		return true;
	}

	/**
	 * Returns the string representation of the HTML Tag Processor.
	 *
	 * @since 6.2.0
	 *
	 * @see WP_HTML_Tag_Processor::get_updated_html()
	 *
	 * @return string The processed HTML.
	 */
	public function __toString(): string {
		return $this->get_updated_html();
	}

	/**
	 * Returns the string representation of the HTML Tag Processor.
	 *
	 * @since 6.2.0
	 * @since 6.2.1 Shifts the internal cursor corresponding to the applied updates.
	 * @since 6.4.0 No longer calls subclass method `next_tag()` after updating HTML.
	 *
	 * @return string The processed HTML.
	 */
	public function get_updated_html(): string {
		$requires_no_updating = 0 === count( $this->classname_updates ) && 0 === count( $this->lexical_updates );

		/*
		 * When there is nothing more to update and nothing has already been
		 * updated, return the original document and avoid a string copy.
		 */
		if ( $requires_no_updating ) {
			return $this->html;
		}

		/*
		 * Keep track of the position right before the current tag. This will
		 * be necessary for reparsing the current tag after updating the HTML.
		 */
		$before_current_tag = $this->token_starts_at ?? 0;

		/*
		 * 1. Apply the enqueued edits and update all the pointers to reflect those changes.
		 */
		$this->class_name_updates_to_attributes_updates();
		$before_current_tag += $this->apply_attributes_updates( $before_current_tag );

		/*
		 * 2. Rewind to before the current tag and reparse to get updated attributes.
		 *
		 * At this point the internal cursor points to the end of the tag name.
		 * Rewind before the tag name starts so that it's as if the cursor didn't
		 * move; a call to `next_tag()` will reparse the recently-updated attributes
		 * and additional calls to modify the attributes will apply at this same
		 * location, but in order to avoid issues with subclasses that might add
		 * behaviors to `next_tag()`, the internal methods should be called here
		 * instead.
		 *
		 * It's important to note that in this specific place there will be no change
		 * because the processor was already at a tag when this was called and it's
		 * rewinding only to the beginning of this very tag before reprocessing it
		 * and its attributes.
		 *
		 * <p>Previous HTML<em>More HTML</em></p>
		 *                 ↑  │ back up by the length of the tag name plus the opening <
		 *                 └←─┘ back up by strlen("em") + 1 ==> 3
		 */
		$this->bytes_already_parsed = $before_current_tag;
		$this->base_class_next_token();

		return $this->html;
	}

	/**
	 * Parses tag query input into internal search criteria.
	 *
	 * @since 6.2.0
	 *
	 * @param array|string|null $query {
	 *     Optional. Which tag name to find, having which class, etc. Default is to find any tag.
	 *
	 *     @type string|null $tag_name     Which tag to find, or `null` for "any tag."
	 *     @type int|null    $match_offset Find the Nth tag matching all search criteria.
	 *                                     1 for "first" tag, 3 for "third," etc.
	 *                                     Defaults to first tag.
	 *     @type string|null $class_name   Tag must contain this class name to match.
	 *     @type string      $tag_closers  "visit" or "skip": whether to stop on tag closers, e.g. </div>.
	 * }
	 */
	private function parse_query( $query ) {
		if ( null !== $query && $query === $this->last_query ) {
			return;
		}

		$this->last_query          = $query;
		$this->sought_tag_name     = null;
		$this->sought_class_name   = null;
		$this->sought_match_offset = 1;
		$this->stop_on_tag_closers = false;

		// A single string value means "find the tag of this name".
		if ( is_string( $query ) ) {
			$this->sought_tag_name = $query;
			return;
		}

		// An empty query parameter applies no restrictions on the search.
		if ( null === $query ) {
			return;
		}

		// If not using the string interface, an associative array is required.
		if ( ! is_array( $query ) ) {
			_doing_it_wrong(
				__METHOD__,
				__( 'The query argument must be an array or a tag name.' ),
				'6.2.0'
			);
			return;
		}

		if ( isset( $query['tag_name'] ) && is_string( $query['tag_name'] ) ) {
			$this->sought_tag_name = $query['tag_name'];
		}

		if ( isset( $query['class_name'] ) && is_string( $query['class_name'] ) ) {
			$this->sought_class_name = $query['class_name'];
		}

		if ( isset( $query['match_offset'] ) && is_int( $query['match_offset'] ) && 0 < $query['match_offset'] ) {
			$this->sought_match_offset = $query['match_offset'];
		}

		if ( isset( $query['tag_closers'] ) ) {
			$this->stop_on_tag_closers = 'visit' === $query['tag_closers'];
		}
	}


	/**
	 * Checks whether a given tag and its attributes match the search criteria.
	 *
	 * @since 6.2.0
	 *
	 * @return bool Whether the given tag and its attribute match the search criteria.
	 */
	private function matches(): bool {
		if ( $this->is_closing_tag && ! $this->stop_on_tag_closers ) {
			return false;
		}

		// Does the tag name match the requested tag name in a case-insensitive manner?
		if (
			isset( $this->sought_tag_name ) &&
			(
				strlen( $this->sought_tag_name ) !== $this->tag_name_length ||
				0 !== substr_compare( $this->html, $this->sought_tag_name, $this->tag_name_starts_at, $this->tag_name_length, true )
			)
		) {
			return false;
		}

		if ( null !== $this->sought_class_name && ! $this->has_class( $this->sought_class_name ) ) {
			return false;
		}

		return true;
	}

	/**
	 * Gets DOCTYPE declaration info from a DOCTYPE token.
	 *
	 * DOCTYPE tokens may appear in many places in an HTML document. In most places, they are
	 * simply ignored. The main parsing functions find the basic shape of DOCTYPE tokens but
	 * do not perform detailed parsing.
	 *
	 * This method can be called to perform a full parse of the DOCTYPE token and retrieve
	 * its information.
	 *
	 * @return WP_HTML_Doctype_Info|null The DOCTYPE declaration information or `null` if not
	 *                                   currently at a DOCTYPE node.
	 */
	public function get_doctype_info(): ?WP_HTML_Doctype_Info {
		if ( self::STATE_DOCTYPE !== $this->parser_state ) {
			return null;
		}

		return WP_HTML_Doctype_Info::from_doctype_token( substr( $this->html, $this->token_starts_at, $this->token_length ) );
	}

	/**
	 * Parser Ready State.
	 *
	 * Indicates that the parser is ready to run and waiting for a state transition.
	 * It may not have started yet, or it may have just finished parsing a token and
	 * is ready to find the next one.
	 *
	 * @since 6.5.0
	 *
	 * @access private
	 */
	const STATE_READY = 'STATE_READY';

	/**
	 * Parser Complete State.
	 *
	 * Indicates that the parser has reached the end of the document and there is
	 * nothing left to scan. It finished parsing the last token completely.
	 *
	 * @since 6.5.0
	 *
	 * @access private
	 */
	const STATE_COMPLETE = 'STATE_COMPLETE';

	/**
	 * Parser Incomplete Input State.
	 *
	 * Indicates that the parser has reached the end of the document before finishing
	 * a token. It started parsing a token but there is a possibility that the input
	 * HTML document was truncated in the middle of a token.
	 *
	 * The parser is reset at the start of the incomplete token and has paused. There
	 * is nothing more than can be scanned unless provided a more complete document.
	 *
	 * @since 6.5.0
	 *
	 * @access private
	 */
	const STATE_INCOMPLETE_INPUT = 'STATE_INCOMPLETE_INPUT';

	/**
	 * Parser Matched Tag State.
	 *
	 * Indicates that the parser has found an HTML tag and it's possible to get
	 * the tag name and read or modify its attributes (if it's not a closing tag).
	 *
	 * @since 6.5.0
	 *
	 * @access private
	 */
	const STATE_MATCHED_TAG = 'STATE_MATCHED_TAG';

	/**
	 * Parser Text Node State.
	 *
	 * Indicates that the parser has found a text node and it's possible
	 * to read and modify that text.
	 *
	 * @since 6.5.0
	 *
	 * @access private
	 */
	const STATE_TEXT_NODE = 'STATE_TEXT_NODE';

	/**
	 * Parser CDATA Node State.
	 *
	 * Indicates that the parser has found a CDATA node and it's possible
	 * to read and modify its modifiable text. Note that in HTML there are
	 * no CDATA nodes outside of foreign content (SVG and MathML). Outside
	 * of foreign content, they are treated as HTML comments.
	 *
	 * @since 6.5.0
	 *
	 * @access private
	 */
	const STATE_CDATA_NODE = 'STATE_CDATA_NODE';

	/**
	 * Indicates that the parser has found an HTML comment and it's
	 * possible to read and modify its modifiable text.
	 *
	 * @since 6.5.0
	 *
	 * @access private
	 */
	const STATE_COMMENT = 'STATE_COMMENT';

	/**
	 * Indicates that the parser has found a DOCTYPE node and it's
	 * possible to read its DOCTYPE information via `get_doctype_info()`.
	 *
	 * @since 6.5.0
	 *
	 * @access private
	 */
	const STATE_DOCTYPE = 'STATE_DOCTYPE';

	/**
	 * Indicates that the parser has found an empty tag closer `</>`.
	 *
	 * Note that in HTML there are no empty tag closers, and they
	 * are ignored. Nonetheless, the Tag Processor still
	 * recognizes them as they appear in the HTML stream.
	 *
	 * These were historically discussed as a "presumptuous tag
	 * closer," which would close the nearest open tag, but were
	 * dismissed in favor of explicitly-closing tags.
	 *
	 * @since 6.5.0
	 *
	 * @access private
	 */
	const STATE_PRESUMPTUOUS_TAG = 'STATE_PRESUMPTUOUS_TAG';

	/**
	 * Indicates that the parser has found a "funky comment"
	 * and it's possible to read and modify its modifiable text.
	 *
	 * Example:
	 *
	 *     </%url>
	 *     </{"wp-bit":"query/post-author"}>
	 *     </2>
	 *
	 * Funky comments are tag closers with invalid tag names. Note
	 * that in HTML these are turn into bogus comments. Nonetheless,
	 * the Tag Processor recognizes them in a stream of HTML and
	 * exposes them for inspection and modification.
	 *
	 * @since 6.5.0
	 *
	 * @access private
	 */
	const STATE_FUNKY_COMMENT = 'STATE_WP_FUNKY';

	/**
	 * Indicates that a comment was created when encountering abruptly-closed HTML comment.
	 *
	 * Example:
	 *
	 *     <!-->
	 *     <!--->
	 *
	 * @since 6.5.0
	 */
	const COMMENT_AS_ABRUPTLY_CLOSED_COMMENT = 'COMMENT_AS_ABRUPTLY_CLOSED_COMMENT';

	/**
	 * Indicates that a comment would be parsed as a CDATA node,
	 * were HTML to allow CDATA nodes outside of foreign content.
	 *
	 * Example:
	 *
	 *     <![CDATA[This is a CDATA node.]]>
	 *
	 * This is an HTML comment, but it looks like a CDATA node.
	 *
	 * @since 6.5.0
	 */
	const COMMENT_AS_CDATA_LOOKALIKE = 'COMMENT_AS_CDATA_LOOKALIKE';

	/**
	 * Indicates that a comment was created when encountering
	 * normative HTML comment syntax.
	 *
	 * Example:
	 *
	 *     <!-- this is a comment -->
	 *
	 * @since 6.5.0
	 */
	const COMMENT_AS_HTML_COMMENT = 'COMMENT_AS_HTML_COMMENT';

	/**
	 * Indicates that a comment would be parsed as a Processing
	 * Instruction node, were they to exist within HTML.
	 *
	 * Example:
	 *
	 *     <?wp __( 'Like' ) ?>
	 *
	 * This is an HTML comment, but it looks like a CDATA node.
	 *
	 * @since 6.5.0
	 */
	const COMMENT_AS_PI_NODE_LOOKALIKE = 'COMMENT_AS_PI_NODE_LOOKALIKE';

	/**
	 * Indicates that a comment was created when encountering invalid
	 * HTML input, a so-called "bogus comment."
	 *
	 * Example:
	 *
	 *     <?nothing special>
	 *     <!{nothing special}>
	 *
	 * @since 6.5.0
	 */
	const COMMENT_AS_INVALID_HTML = 'COMMENT_AS_INVALID_HTML';

	/**
	 * No-quirks mode document compatibility mode.
	 *
	 * > In no-quirks mode, the behavior is (hopefully) the desired behavior
	 * > described by the modern HTML and CSS specifications.
	 *
	 * @see self::$compat_mode
	 * @see https://developer.mozilla.org/en-US/docs/Web/HTML/Quirks_Mode_and_Standards_Mode
	 *
	 * @since 6.7.0
	 *
	 * @var string
	 */
	const NO_QUIRKS_MODE = 'no-quirks-mode';

	/**
	 * Quirks mode document compatibility mode.
	 *
	 * > In quirks mode, layout emulates behavior in Navigator 4 and Internet
	 * > Explorer 5. This is essential in order to support websites that were
	 * > built before the widespread adoption of web standards.
	 *
	 * @see self::$compat_mode
	 * @see https://developer.mozilla.org/en-US/docs/Web/HTML/Quirks_Mode_and_Standards_Mode
	 *
	 * @since 6.7.0
	 *
	 * @var string
	 */
	const QUIRKS_MODE = 'quirks-mode';

	/**
	 * Indicates that a span of text may contain any combination of significant
	 * kinds of characters: NULL bytes, whitespace, and others.
	 *
	 * @see self::$text_node_classification
	 * @see self::subdivide_text_appropriately
	 *
	 * @since 6.7.0
	 */
	const TEXT_IS_GENERIC = 'TEXT_IS_GENERIC';

	/**
	 * Indicates that a span of text comprises a sequence only of NULL bytes.
	 *
	 * @see self::$text_node_classification
	 * @see self::subdivide_text_appropriately
	 *
	 * @since 6.7.0
	 */
	const TEXT_IS_NULL_SEQUENCE = 'TEXT_IS_NULL_SEQUENCE';

	/**
	 * Indicates that a span of decoded text comprises only whitespace.
	 *
	 * @see self::$text_node_classification
	 * @see self::subdivide_text_appropriately
	 *
	 * @since 6.7.0
	 */
	const TEXT_IS_WHITESPACE = 'TEXT_IS_WHITESPACE';

	/**
	 * Wakeup magic method.
	 *
	 * @since 6.9.2
	 */
	public function __wakeup() {
		throw new \LogicException( __CLASS__ . ' should never be unserialized' );
	}
}