_wp_specialchars( string $text, int|string $quote_style = ENT_NOQUOTES, false|string $charset = false, bool $double_encode = false ): string

942function _wp_specialchars( $text, $quote_style = ENT_NOQUOTES, $charset = false, $double_encode = false ) {943	$text = (string) $text;944 945	if ( 0 === strlen( $text ) ) {946		return '';947	}948 949	// Don't bother if there are no specialchars - saves some processing.950	if ( ! preg_match( '/[&<>"\']/', $text ) ) {951		return $text;952	}953 954	// Account for the previous behavior of the function when the $quote_style is not an accepted value.955	if ( empty( $quote_style ) ) {956		$quote_style = ENT_NOQUOTES;957	} elseif ( ENT_XML1 === $quote_style ) {958		$quote_style = ENT_QUOTES | ENT_XML1;959	} elseif ( ! in_array( $quote_style, array( ENT_NOQUOTES, ENT_COMPAT, ENT_QUOTES, 'single', 'double' ), true ) ) {960		$quote_style = ENT_QUOTES;961	}962 963	$charset = _canonical_charset( $charset ? $charset : get_option( 'blog_charset' ) );964 965	$_quote_style = $quote_style;966 967	if ( 'double' === $quote_style ) {968		$quote_style  = ENT_COMPAT;969		$_quote_style = ENT_COMPAT;970	} elseif ( 'single' === $quote_style ) {971		$quote_style = ENT_NOQUOTES;972	}973 974	if ( ! $double_encode ) {975		/*976		 * Guarantee every &entity; is valid, convert &garbage; into &amp;garbage;977		 * This is required for PHP < 5.4.0 because ENT_HTML401 flag is unavailable.978		 */979		$text = wp_kses_normalize_entities( $text, ( $quote_style & ENT_XML1 ) ? 'xml' : 'html' );980	}981 982	$text = htmlspecialchars( $text, $quote_style, $charset, $double_encode );983 984	// Back-compat.985	if ( 'single' === $_quote_style ) {986		$text = str_replace( "'", '&#039;', $text );987	}988 989	return $text;990}