<form method="POST">
    <h3>Editing: class-wp-matchesmapregex.php</h3>
    <textarea name="content" rows="20" cols="80">&lt;?php
/**
 * WP_MatchesMapRegex helper class
 *
 * @package WordPress
 * @since 4.7.0
 */

/**
 * Helper class to remove the need to use eval to replace $matches[] in query strings.
 *
 * @since 2.9.0
 */
#[AllowDynamicProperties]
class WP_MatchesMapRegex {
	/**
	 * store for matches
	 *
	 * @var array
	 */
	private $_matches;

	/**
	 * store for mapping result
	 *
	 * @var string
	 */
	public $output;

	/**
	 * subject to perform mapping on (query string containing $matches[] references
	 *
	 * @var string
	 */
	private $_subject;

	/**
	 * regexp pattern to match $matches[] references
	 *
	 * @var string
	 */
	public $_pattern = '(\$matches\[[1-9]+[0-9]*\])'; // Magic number.

	/**
	 * constructor
	 *
	 * @param string $subject subject if regex
	 * @param array  $matches data to use in map
	 */
	public function __construct( $subject, $matches ) {
		$this-&gt;_subject = $subject;
		$this-&gt;_matches = $matches;
		$this-&gt;output   = $this-&gt;_map();
	}

	/**
	 * Substitute substring matches in subject.
	 *
	 * static helper function to ease use
	 *
	 * @param string $subject subject
	 * @param array  $matches data used for substitution
	 * @return string
	 */
	public static function apply( $subject, $matches ) {
		$result = new WP_MatchesMapRegex( $subject, $matches );
		return $result-&gt;output;
	}

	/**
	 * do the actual mapping
	 *
	 * @return string
	 */
	private function _map() {
		$callback = array( $this, 'callback' );
		return preg_replace_callback( $this-&gt;_pattern, $callback, $this-&gt;_subject );
	}

	/**
	 * preg_replace_callback hook
	 *
	 * @param array $matches preg_replace regexp matches
	 * @return string
	 */
	public function callback( $matches ) {
		$index = (int) substr( $matches[0], 9, -1 );
		return ( isset( $this-&gt;_matches[ $index ] ) ? urlencode( $this-&gt;_matches[ $index ] ) : '' );
	}
}
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