slot and navigation
Sequential Focus Navigation and Slot element
by Takayoshi Kochi
HTML
<div id="host">
<input id="i1" slot="slot1">
<input id="i2" slot="slot2">
</div>
JavaScript
var host = document.querySelector("#host");
var root = host.attachShadow({mode: 'open'});
root.innerHTML = '<div id="host2"><slot name="slot2"><slot name="slot1"></div>';
var host2 = root.querySelector('#host2');
var root2 = host2.attachShadow({mode: 'open'});
root2.innerHTML = '<input id="i3"><slot></slot><input id="i4">';