code: function assignedNodesChanged(component) {
  
    const slot = component[symbols.contentSlot];
    const content = slot ?
      slot.assignedNodes({ flatten: true }) :
      null;
  
    // Make immutable.
    Object.freeze(content);
    
    component.setState({ content });
  }
docs: The nodes assigned to the given component have changed. Update the component's state to reflect the new content.