New "modal" feature

data-toggle-modal

Specify that the target is a modal, such as a dialog or a lightbox. This way, when the target is active – open –, the focus is trapped inside this target. This means tabbing will only focus on focusable elements inside this target, letting anything outside be out of scope.

Be really careful when using this feature. A focus trap can be very annoying – and an accessibility fault – when used in a wrong way, so be sure your target is a modal component.