public function error($string, $level = null)
    {
        $this->out->level($level)->writeln("<error>$string</error>");
        
        return $this;
    }
public function error($string, $level = null)
    {
        $this->out->level($level)->writeln("<error>$string</error>");
        
        return $this;
    }
public function error ( $ string , $ level = null ) { $ this -> out -> level ( $ level ) -> writeln ( "<error>$string</error>" ) ; return $ this ; }
Write a string as error output.

@param  string  $string
@param  int     $level
@return \CupOfTea\TwoStream\Console\Writer
Write a string as error output .