Changelog

PanelGroup, Panel, PanelResizeHandle, and an optional PanelProvider for building docked and peer panel layouts with pointer, touch, and keyboard resizing. A standalone PanelGroup installs an implicit provider, so the explicit PanelProvider is only needed to share state across groups.

Docked and peer panels with nested groups and per-axis relative sizing. Docked panels collapse animated, instantly, or to a collapsedSize rail, and collapseBelow thresholds close a panel mid-drag with hysteresis and a configurable close behavior.

A group-level animation prop disables all library-owned transitions or overrides the default 300ms duration and easing per group.

Sibling drag cascades with a cascade prop choosing mid-drag reversal semantics — "reversible" retraces the cascade exactly, "latching" keeps far panels pushed until released space reaches them. Per panel, disabled blocks all resizing and pinned exempts a docked panel from other handles' cascades.

A per-panel containerResizeBehavior ("fixed" or "proportional") decides how expanded panels respond when the group's container changes size.

A PanelGroupValue state model with controlled and uncontrolled modes. onValueChange reports reason and trigger metadata, and is kept separate from the pointer resize lifecycle exposed through onResizeStart and onResizeEnd.

Imperative apiRef controllers (PanelApi, PanelGroupApi) alongside locator-keyed hooks: usePanelControls, usePanelActions, usePanelRegistry, usePanelCollapsed, usePanelInteractionState, and usePanelGroupState. Action results are authoritative and report the value the group actually accepted.

A grouped persistence option with read, deserialize, and write error reporting plus restore-status callbacks.

A strict, CSS-compatible SizeSpec grammar with field-specific fallbacks and development-only diagnostics.

Handles implement the ARIA separator pattern (aria-valuenow, min, max, aria-controls, aria-orientation) and resize with the arrow keys, Home, and End, at full parity with pointer gestures.

Right-to-left layouts via dir="rtl" on the group, touch and pointer input, and SSR-safe rendering.