protected function serializeCharacterClass(array $values)
	{
		$expr = '[';
		foreach ($this->getRanges($values) as list($start, $end))
		{
			$expr .= $this->serializeCharacterClassUnit($start);
			if ($end > $start)
			{
				if ($end > $start + 1)
				{
					$expr .= '-';
				}
				$expr .= $this->serializeCharacterClassUnit($end);
			}
		}
		$expr .= ']';

		return $expr;
	}