Method addChild

packages/react-aria/src/focus/FocusScope.tsx:1111–1114

(node: TreeNode)

    this.scopeRef = props.scopeRef;
  }
  addChild(node: TreeNode): void {
    this.children.add(node);
    node.parent = this;
  }
  removeChild(node: TreeNode): void {
    this.children.delete(node);
    node.parent = undefined;