Tabs & disclosure
Pills switch views inside a canvas; underline reads as document navigation.
Underline
Page-level sub-navigation — the treatment docs pages use.
Overview panel.
Pills
Switching views inside a canvas — both measured references use pills here.
All.
Accordion
Several sections that open and close in place.
Why
The panel animates with the 0fr → 1fr grid trick: height:auto is not animatable, and max-height guessing gives a clipped panel or a visible pause.
Collapsible
One panel, one trigger — no set, no single-open rule. That is the whole difference from Accordion.