constructor(props) {
        super(props);
        this.containerRef = React.createRef();
        this.buttonRef = React.createRef();
        this.modalRef = React.createRef();
        this.contentRef = React.createRef();
        this.modalHeadingId = uniqueId('modal-heading');
        this.modalContentId = uniqueId('modal-content');
        this.handleKeyPressed = this.handleKeyPressed.bind(this);
        this.handleClick = this.handleClick.bind(this);
        this.closeModal = this.closeModal.bind(this);
        this.addBackdropClickListener = this.addBackdropClickListener.bind(this);
        this.removeBackdropClickListener = this.removeBackdropClickListener.bind(this);
    }
Modals are used to display content in a layer above the app.
This is used in cases such as the creation or editing of a record,
as well as various types of messaging.
@category Layout