protected function update_unit_pattern( array $units ) {
		// Update unit regex pattern.
		foreach ( $units as $index => $unit ) {
			$units[ $index ] = \preg_quote( $unit, '/' );
		}

		$custom_units  = \implode( '|', $units );
		$custom_units .= ! empty( $custom_units ) ? '|' : '';

		return $custom_units;
	}