SPACEkey must open lightbox dialog.
SHIFT-TABto focusable elements of child window.
ESCkey must close lightbox dialog (unless the currently focussed element has existing
aria-haspopup="true"is not valid in this context).
hiddento prevent it from being displayed on page load.
aria-hidden="true"to any non direct-ancestor nodes in the DOM.
overflow:hiddento the html body.
ESCkey while focus is on the dismiss button, or any other interactive element that does not already have
ESCkey behaviour, should close the dialog.
ESCevent from bubbling.
dialog-closeis a custom event fired by the lightbox dialog widget.