esc_xml( string $text ): string

4751function esc_xml( $text ) {4752	$safe_text = wp_check_invalid_utf8( $text );4753 4754	$cdata_regex = '\<\!\[CDATA\[.*?\]\]\>';4755	$regex       = <<<EOF4756/4757	(?=.*?{$cdata_regex})                 # lookahead that will match anything followed by a CDATA Section4758	(?<non_cdata_followed_by_cdata>(.*?)) # the "anything" matched by the lookahead4759	(?<cdata>({$cdata_regex}))            # the CDATA Section matched by the lookahead4760 4761|	                                      # alternative4762 4763	(?<non_cdata>(.*))                    # non-CDATA Section4764/sx4765EOF;4766 4767	$safe_text = (string) preg_replace_callback(4768		$regex,4769		static function ( $matches ) {4770			if ( ! isset( $matches[0] ) ) {4771				return '';4772			}4773 4774			if ( isset( $matches['non_cdata'] ) ) {4775				// escape HTML entities in the non-CDATA Section.4776				return _wp_specialchars( $matches['non_cdata'], ENT_XML1 );4777			}4778 4779			// Return the CDATA Section unchanged, escape HTML entities in the rest.4780			return _wp_specialchars( $matches['non_cdata_followed_by_cdata'], ENT_XML1 ) . $matches['cdata'];4781		},4782		$safe_text4783	);4784 4785	/**4786	 * Filters a string cleaned and escaped for output in XML.4787	 *4788	 * Text passed to esc_xml() is stripped of invalid or special characters4789	 * before output. HTML named character references are converted to their4790	 * equivalent code points.4791	 *4792	 * @since 5.5.04793	 *4794	 * @param string $safe_text The text after it has been escaped.4795	 * @param string $text      The text prior to being escaped.4796	 */4797	return apply_filters( 'esc_xml', $safe_text, $text );4798}
When	Instructions	Calls it makes
`!isset($matches)`	4	none
`isset($matches)`	12–14	`_wp_specialchars()`