mmo-tabs
Tabs over panes that are written flat: a tab carries target-id, the pane it shows
carries that id, so a pane can be anything — including another mmo-tabs.
Usage
The tabs and the panes are slotted separately, so the markup never nests one inside the other.
The first tab is the one that opens, unless one carries class="active".
The strip is the design system's, not a copy of it: a segmented track with the active tab filled
with the accent, the same thing .tabs paints in a page. class="line"
switches to the quiet form — tabs on a rule, the active one breaking it — for a strip
that navigates rather than switches.
Examples
This page is itself a pair of tabs, and the example above is a second pair inside one of its panes: each element only ever looks at its own children.