# Thread Slots

`data.avatarSlot` and `data.headerSlot` are page fills `(host, context) => cleanup?` created once and kept across every update. The branch tabs are a real tablist: `role="tab"`, `aria-selected`, a roving tab stop and Left/Right (Home, End) to move, following the reading direction. `labels` rewords any built-in word; the locale pack answers first when a key is not set.