public function setHeader($key, $value = null, $preserveCase = false)
	{
		if ($value === null) {
			list($key, $value) = explode(':', $value, 2);
		}

		if (!$preserveCase) {
			$key = strtolower($key);
		}
		
		$key = trim($key);
		$this->headers[$key] = trim($value);

		return $this;
	}