public function setMargin($margin = 0) {
		$margin = $this->parseSizes($margin);

		foreach ($margin as $side => $value) {
			if (! is_int($value) || $value < 0) {
				throw new InvalidArgumentException(sprintf(
					'Invalid %s margin: "%s". Must be a positive integer value.',
					$side, $value
				));
			}

			$this->margin[$side] = $value;
		}
	}