_wp_timezone_choice_usort_callback() WordPress Function

function _wp_timezone_choice_usort_callback( $a, $b ) {
	// Don't use translated versions of Etc.
	if ( 'Etc' === $a['continent'] && 'Etc' === $b['continent'] ) {
		// Make the order of these more like the old dropdown.
		if ( 'GMT+' === substr( $a['city'], 0, 4 ) && 'GMT+' === substr( $b['city'], 0, 4 ) ) {
			return -1 * ( strnatcasecmp( $a['city'], $b['city'] ) );
		}
		if ( 'UTC' === $a['city'] ) {
			if ( 'GMT+' === substr( $b['city'], 0, 4 ) ) {
				return 1;
			}
			return -1;
		}
		if ( 'UTC' === $b['city'] ) {
			if ( 'GMT+' === substr( $a['city'], 0, 4 ) ) {
				return -1;
			}
			return 1;
		}
		return strnatcasecmp( $a['city'], $b['city'] );
	}
	if ( $a['t_continent'] == $b['t_continent'] ) {
		if ( $a['t_city'] == $b['t_city'] ) {
			return strnatcasecmp( $a['t_subcity'], $b['t_subcity'] );
		}
		return strnatcasecmp( $a['t_city'], $b['t_city'] );
	} else {
		// Force Etc to the bottom of the list.
		if ( 'Etc' === $a['continent'] ) {
			return 1;
		}
		if ( 'Etc' === $b['continent'] ) {
			return -1;
		}
		return strnatcasecmp( $a['t_continent'], $b['t_continent'] );
	}
}