showModal(title, children, ...classes) {
		const dlg = modalDiv.firstElementChild;

		dlg.setAttribute('class', 'modal');
		dlg.classList.add(...classes);

		dom.content(dlg, dom.create('h4', {}, title));
		dom.append(dlg, children);

		document.body.classList.add('modal-overlay-active');
		modalDiv.scrollTop = 0;
		modalDiv.focus();

		return dlg;
	}
Display a modal overlay dialog with the specified contents.

The modal overlay dialog covers the current view preventing interaction
with the underlying view contents. Only one modal dialog instance can
be opened. Invoking showModal() while a modal dialog is already open will
replace the open dialog with a new one having the specified contents.

Additional CSS class names may be passed to influence the appearance of
the dialog. Valid values for the classes depend on the underlying theme.

@see LuCI.dom.content

@param {string} [title]
The title of the dialog. If `null`, no title element will be rendered.

@param {*} children
The contents to add to the modal dialog. This should be a DOM node or
a document fragment in most cases. The value is passed as-is to the
`dom.content()` function - refer to its documentation for applicable
values.

@param {...string} [classes]
A number of extra CSS class names which are set on the modal dialog
element.

@returns {Node}
Returns a DOM Node representing the modal dialog element.