This is a small, focused React component library that wraps the native ResizeObserver API. It provides a declarative component (`<ResizeObserver>`) that can observe a single child element for size changes, supporting both direct children and render-prop patterns for cases where the observed element is not the immediate child. A `Collection` component uses React context and microtask batching to aggregate multiple resize events from child observers into a single callback, improving performance when many elements are observed. The library also exports a `useResizeObserver` hook for imperative use. Internally, it manages a single shared `ResizeObserver` instance with a map of element-to-callback sets, ensuring efficient resource usage. The code is clean, well-typed, and properly tested, making it a reliable building block for responsive UIs. As part of the Ant Design ecosystem, it follows established patterns and integrates smoothly with other @rc-component packages.