Navigation
Collapsible
A single show/hide disclosure. Use it for one optional region; for a set of them use Accordion.
Not documented yet
This component ships in the design system and is fully supported. What is missing is the guidance around it: when to reach for it, the do and don't, and the accessibility notes. Until that is written, Storybook is the reference for variants, props and live controls.
MenubarPlanned
A horizontal application menu bar. Rare in the product UI; it exists for dense internal tools that expect desktop conventions.
Dialog
A modal window for a focused task — editing a record, previewing a document, a short form. It traps focus, returns it to the trigger on close, and can be dismissed by overlay click, Esc or the × button.