 In ShadowDOM v1, tab order is affected by the order of distrubution.
        // E.g. getTabbableNodes(#root) in ShadowDOM v1 should return [#A, #B];
        // in ShadowDOM v0 tab order is not affected by the distrubution order,
        // in fact getTabbableNodes(#root) returns [#B, #A].
        //  <div id="root">
        //   <!-- shadow -->
        //     <slot name="a">
        //     <slot name="b">
        //   <!-- /shadow -->
        //   <input id="A" slot="a">
        //   <input id="B" slot="b"