public function setAxis($axis)
    {
        if (is_string($axis) === true) {
            $this->axis = $axis;
        } else {
            $msg = "The 'axis' argument must be a string, '" . gettype($axis) . "' given.";
            throw new InvalidArgumentException($msg);
        }
    }
public function setAxis($axis)
    {
        if (is_string($axis) === true) {
            $this->axis = $axis;
        } else {
            $msg = "The 'axis' argument must be a string, '" . gettype($axis) . "' given.";
            throw new InvalidArgumentException($msg);
        }
    }
public function setAxis ( $ axis ) { if ( is_string ( $ axis ) === true ) { $ this -> axis = $ axis ; } else { $ msg = "The 'axis' argument must be a string, '" . gettype ( $ axis ) . "' given." ; throw new InvalidArgumentException ( $ msg ) ; } }
Set the value of the axis attribute.

@param string $axis A string. Give an empty string if no axis is indicated.
@throws \InvalidArgumentException If $axis is not a string.
Set the value of the axis attribute .