OptionalbuttonsOptionalcontainerOptionalcontextOptionalgrowOptionalkeepKeep the body in the DOM when collapsed (hidden via CSS) instead of unmounting it. Use for a stateful widget whose content shouldn't be rebuilt on every collapse — e.g. the sidebar chat, whose live conversation, draft input, and DOM-attached listeners would otherwise be torn down and (because its hooks live in the always-mounted parent) not re-wired on expand.
OptionalnoAdd no padding to the widget body.
Take the height the other widgets of the tab leave over, scrolling the body within it, instead of keeping to the height of the content. Use for the one widget a tab is really about — a note's own attributes, its table of contents, the chat — so that the rest keep to their content around it.
Two of them in a tab share the leftover height between them, each keeping its own floor — a PDF's outline and its pages. Ask for it once more than that and none of them is left with room worth having. It lapses while the widget is collapsed, so the others move up to fill the room.