Hi I have 2 questions: First, in React bootstrap there is often used Xml like variable, but it has no value:

            <Bs.Modal
            show={this.state.isVisible}
            // onHide={this.props.onHide}
            scrollable={true}
            size="lg"
            aria-labelledby="contained-modal-title-vcenter"
            centered></Bs.Modal>

        

In this case its last attribute centered and I would like to ask how is this "undefined" variable called. And second question is, how to make this variable switchable, like {isCenteredtype && center}