setButtons(buttons) {
        const me = this,
            container = me._container;

        me._buttons = buttons;
        if (container) {
            const buttonGroup = container.querySelector('#panel-button-group'),
                children = buttonGroup.children;

            for (let i = children.length - 1; i > 0; i--) {
                buttonGroup.removeChild(children[i]);
            }
            for (const button of buttons || []) {
                buttonGroup.appendChild(button);
            }
        }

        return me;
    }
Sets buttons on the panel's title.
@param {Array<HTMLElement>} buttons - An array of DOM elements to use as buttons
    on the title of the panel
@returns {Panel} Returns itself to allow for method chaining