public function header($header, $value = null)
	{
		if(is_array($header))
		{
			foreach($header as $_header => $_value)
			{
				empty($_value) or $this->extra_headers[$_header] = $_value;
			}
		}
		else
		{
			empty($value) or $this->extra_headers[$header] = $value;
		}

		return $this;
	}