<bmx-tab-panel>
One panel inside a bmx-tabs, and the whole of what an author writes.
A panel is an ordinary element holding ordinary content. It shows when its tab is chosen.
badge takes any short string, not only a number.
Unreachable while it is disabled.
A panel is only ever inside a
bmx-tabs: it carries the label the tab is drawn from, and the tabs element
decides which one is showing.
Every property, event and method: https://docs.binarymission.co.uk/webcomponents/bmx/bmx-tab-panel.html