force_balance_tags( string $text )

Balances tags of string using a modified stack.


Description Description


Parameters Parameters

$text

(string) (Required) Text to be balanced.


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Return Return

(string) Balanced text.


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Source Source

File: wp-includes/formatting.php

function force_balance_tags( $text ) {
	$tagstack  = array();
	$stacksize = 0;
	$tagqueue  = '';
	$newtext   = '';
	// Known single-entity/self-closing tags.
	$single_tags = array( 'area', 'base', 'basefont', 'br', 'col', 'command', 'embed', 'frame', 'hr', 'img', 'input', 'isindex', 'link', 'meta', 'param', 'source' );
	// Tags that can be immediately nested within themselves.
	$nestable_tags = array( 'blockquote', 'div', 'object', 'q', 'span' );

	// WP bug fix for comments - in case you REALLY meant to type '< !--'.
	$text = str_replace( '< !--', '<    !--', $text );
	// WP bug fix for LOVE <3 (and other situations with '<' before a number).
	$text = preg_replace( '#<([0-9]{1})#', '&lt;$1', $text );

	/**
	 * Matches supported tags.
	 *
	 * To get the pattern as a string without the comments paste into a PHP
	 * REPL like `php -a`.
	 *
	 * @see https://html.spec.whatwg.org/#elements-2
	 * @see https://w3c.github.io/webcomponents/spec/custom/#valid-custom-element-name
	 *
	 * @example
	 * ~# php -a
	 * php > $s = [paste copied contents of expression below including parentheses];
	 * php > echo $s;
	 */
	$tag_pattern = (
		'#<' . // Start with an opening bracket.
		'(/?)' . // Group 1 - If it's a closing tag it'll have a leading slash.
		'(' . // Group 2 - Tag name.
			// Custom element tags have more lenient rules than HTML tag names.
			'(?:[a-z](?:[a-z0-9._]*)-(?:[a-z0-9._-]+)+)' .
				'|' .
			// Traditional tag rules approximate HTML tag names.
			'(?:[\w:]+)' .
		')' .
		'(?:' .
			// We either immediately close the tag with its '>' and have nothing here.
			'\s*' .
			'(/?)' . // Group 3 - "attributes" for empty tag.
				'|' .
			// Or we must start with space characters to separate the tag name from the attributes (or whitespace).
			'(\s+)' . // Group 4 - Pre-attribute whitespace.
			'([^>]*)' . // Group 5 - Attributes.
		')' .
		'>#' // End with a closing bracket.
	);

	while ( preg_match( $tag_pattern, $text, $regex ) ) {
		$full_match        = $regex[0];
		$has_leading_slash = ! empty( $regex[1] );
		$tag_name          = $regex[2];
		$tag               = strtolower( $tag_name );
		$is_single_tag     = in_array( $tag, $single_tags, true );
		$pre_attribute_ws  = isset( $regex[4] ) ? $regex[4] : '';
		$attributes        = trim( isset( $regex[5] ) ? $regex[5] : $regex[3] );
		$has_self_closer   = '/' === substr( $attributes, -1 );

		$newtext .= $tagqueue;

		$i = strpos( $text, $full_match );
		$l = strlen( $full_match );

		// Clear the shifter.
		$tagqueue = '';
		if ( $has_leading_slash ) { // End tag.
			// If too many closing tags.
			if ( $stacksize <= 0 ) {
				$tag = '';
				// Or close to be safe $tag = '/' . $tag.

				// If stacktop value = tag close value, then pop.
			} elseif ( $tagstack[ $stacksize - 1 ] === $tag ) { // Found closing tag.
				$tag = '</' . $tag . '>'; // Close tag.
				array_pop( $tagstack );
				$stacksize--;
			} else { // Closing tag not at top, search for it.
				for ( $j = $stacksize - 1; $j >= 0; $j-- ) {
					if ( $tagstack[ $j ] === $tag ) {
						// Add tag to tagqueue.
						for ( $k = $stacksize - 1; $k >= $j; $k-- ) {
							$tagqueue .= '</' . array_pop( $tagstack ) . '>';
							$stacksize--;
						}
						break;
					}
				}
				$tag = '';
			}
		} else { // Begin tag.
			if ( $has_self_closer ) { // If it presents itself as a self-closing tag...
				// ...but it isn't a known single-entity self-closing tag, then don't let it be treated as such
				// and immediately close it with a closing tag (the tag will encapsulate no text as a result).
				if ( ! $is_single_tag ) {
					$attributes = trim( substr( $attributes, 0, -1 ) ) . "></$tag";
				}
			} elseif ( $is_single_tag ) { // Else if it's a known single-entity tag but it doesn't close itself, do so.
				$pre_attribute_ws = ' ';
				$attributes      .= '/';
			} else { // It's not a single-entity tag.
				// If the top of the stack is the same as the tag we want to push, close previous tag.
				if ( $stacksize > 0 && ! in_array( $tag, $nestable_tags, true ) && $tagstack[ $stacksize - 1 ] === $tag ) {
					$tagqueue = '</' . array_pop( $tagstack ) . '>';
					$stacksize--;
				}
				$stacksize = array_push( $tagstack, $tag );
			}

			// Attributes.
			if ( $has_self_closer && $is_single_tag ) {
				// We need some space - avoid <br/> and prefer <br />.
				$pre_attribute_ws = ' ';
			}

			$tag = '<' . $tag . $pre_attribute_ws . $attributes . '>';
			// If already queuing a close tag, then put this tag on too.
			if ( ! empty( $tagqueue ) ) {
				$tagqueue .= $tag;
				$tag       = '';
			}
		}
		$newtext .= substr( $text, 0, $i ) . $tag;
		$text     = substr( $text, $i + $l );
	}

	// Clear tag queue.
	$newtext .= $tagqueue;

	// Add remaining text.
	$newtext .= $text;

	while ( $x = array_pop( $tagstack ) ) {
		$newtext .= '</' . $x . '>'; // Add remaining tags to close.
	}

	// WP fix for the bug with HTML comments.
	$newtext = str_replace( '< !--', '<!--', $newtext );
	$newtext = str_replace( '<    !--', '< !--', $newtext );

	return $newtext;
}

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Changelog Changelog

Changelog
Version Description
5.3.0 Improve accuracy and add support for custom element tags.
2.0.4 Introduced.


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User Contributed Notes User Contributed Notes

  1. Skip to note 1 content
    Contributed by Codex

    Basic Usage

    <?php force_balance_tags( $text ) ?>
    

    This function is used in the short post excerpt list, to prevent unmatched elements. For example, it makes

    <div><b>This is an excerpt. <!--more--> and this is more text... </b></div>
    

    not break, when the html after the more tag is cut off.

    <div><b>This is an excerpt. 
    

    should be changed to:

    <div><b>This is an excerpt. </b></div>
    

    by the force_balance_tags function.

  2. Skip to note 2 content
    Contributed by Codex

    Basic Usage

    <?php force_balance_tags( $text ) ?>
    

    This function is used in the short post excerpt list, to prevent unmatched elements.
    For example, it makes

    This is an excerpt. and this is more text...

    not break, when the html after the more tag is cut off.

    This is an excerpt.

    should be changed to:

    This is an excerpt.

    by the force_balance_tags function.

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