public function header( $key, $value = null ) {

		$key = explode( '-', $key );
		foreach( $key as $k => $v ) {
			$key[$k] = ucfirst( strtolower($v));
		}
		$key = implode( '-', $key );

		if ( !is_null( $value ) ) {
			$this->_headers[$key] = $value;
		}

		return $this->_headers[$key];
	}