public function usage(string $usage = null)
    {
        if (\func_num_args() === 0) {
            return $this->_usage;
        }

        $this->_usage = $usage;

        return $this;
    }
public function usage(string $usage = null)
    {
        if (\func_num_args() === 0) {
            return $this->_usage;
        }

        $this->_usage = $usage;

        return $this;
    }
public function usage ( string $ usage = null ) { if ( \ func_num_args ( ) === 0 ) { return $ this -> _usage ; } $ this -> _usage = $ usage ; return $ this ; }
Gets or sets usage info.

@param string|null $usage

@return string|self
Gets or sets usage info .