force_balance_tags( string $text ): string

2592function force_balance_tags( $text ) {2593	$tagstack  = array();2594	$stacksize = 0;2595	$tagqueue  = '';2596	$newtext   = '';2597	// Known single-entity/self-closing tags.2598	$single_tags = array( 'area', 'base', 'basefont', 'br', 'col', 'command', 'embed', 'frame', 'hr', 'img', 'input', 'isindex', 'link', 'meta', 'param', 'source', 'track', 'wbr' );2599	// Tags that can be immediately nested within themselves.2600	$nestable_tags = array( 'article', 'aside', 'blockquote', 'details', 'div', 'figure', 'object', 'q', 'section', 'span' );2601 2602	// WP bug fix for comments - in case you REALLY meant to type '< !--'.2603	$text = str_replace( '< !--', '<    !--', $text );2604	// WP bug fix for LOVE <3 (and other situations with '<' before a number).2605	$text = preg_replace( '#<([0-9]{1})#', '&lt;$1', $text );2606 2607	/**2608	 * Matches supported tags.2609	 *2610	 * To get the pattern as a string without the comments paste into a PHP2611	 * REPL like `php -a`.2612	 *2613	 * @see https://html.spec.whatwg.org/#elements-22614	 * @see https://html.spec.whatwg.org/multipage/custom-elements.html#valid-custom-element-name2615	 *2616	 * @example2617	 * ~# php -a2618	 * php > $s = [paste copied contents of expression below including parentheses];2619	 * php > echo $s;2620	 */2621	$tag_pattern = (2622		'#<' . // Start with an opening bracket.2623		'(/?)' . // Group 1 - If it's a closing tag it'll have a leading slash.2624		'(' . // Group 2 - Tag name.2625			// Custom element tags have more lenient rules than HTML tag names.2626			'(?:[a-z](?:[a-z0-9._]*)-(?:[a-z0-9._-]+)+)' .2627				'|' .2628			// Traditional tag rules approximate HTML tag names.2629			'(?:[\w:]+)' .2630		')' .2631		'(?:' .2632			// We either immediately close the tag with its '>' and have nothing here.2633			'\s*' .2634			'(/?)' . // Group 3 - "attributes" for empty tag.2635				'|' .2636			// Or we must start with space characters to separate the tag name from the attributes (or whitespace).2637			'(\s+)' . // Group 4 - Pre-attribute whitespace.2638			'([^>]*)' . // Group 5 - Attributes.2639		')' .2640		'>#' // End with a closing bracket.2641	);2642 2643	while ( preg_match( $tag_pattern, $text, $regex ) ) {2644		$full_match        = $regex[0];2645		$has_leading_slash = ! empty( $regex[1] );2646		$tag_name          = $regex[2];2647		$tag               = strtolower( $tag_name );2648		$is_single_tag     = in_array( $tag, $single_tags, true );2649		$pre_attribute_ws  = $regex[4] ?? '';2650		$attributes        = trim( $regex[5] ?? $regex[3] );2651		$has_self_closer   = str_ends_with( $attributes, '/' );2652 2653		$newtext .= $tagqueue;2654 2655		$i = strpos( $text, $full_match );2656		$l = strlen( $full_match );2657 2658		// Clear the shifter.2659		$tagqueue = '';2660		if ( $has_leading_slash ) { // End tag.2661			// If too many closing tags.2662			if ( $stacksize <= 0 ) {2663				$tag = '';2664				// Or close to be safe $tag = '/' . $tag.2665 2666				// If stacktop value = tag close value, then pop.2667			} elseif ( $tagstack[ $stacksize - 1 ] === $tag ) { // Found closing tag.2668				$tag = '</' . $tag . '>'; // Close tag.2669				array_pop( $tagstack );2670				--$stacksize;2671			} else { // Closing tag not at top, search for it.