public function priority($level = 1) {

		if(false === ('-' . intval($level) == '-' . $level)) {
			return trigger_error(sprintf('Argument 1 passed to %s() must be of the type integer, "%s" given', __METHOD__, gettype($level)), E_USER_ERROR);
		}

		if($level < 1 || $level > 5) {
			return trigger_error(sprintf('Argument 1 passed to %s() should be between 1 and 5, "%s" given', __METHOD__, $level), E_USER_ERROR);	
		}

		$priorities = [
			
			1 => ['1 (Highest)', 'High', 'High'],
			2 => ['2 (High)', 'High', 'High'],
			3 => ['3 (Normal)', 'Normal', 'Normal'],
			4 => ['4 (Low)', 'Low', 'Low'],
			5 => ['5 (Lowest)', 'Low', 'Low'],
		];

		$this -> headers['priority'] = $priorities[$level];

		return $this;
	}