Closed mode creates a Shadow DOM boundary whose shadow root is not exposed through the host element’s standard `shadowRoot` property. It helps block ordinary outside access to a component’s internal DOM, but it is aimed at accidental intrusion rather than strong protection against malicious users. section 8.2 section 8.4
Create a closed shadow root
Use the returned root immediately instead of reading it back from the host: `connectedCallback() { const root = this.attachShadow({ mode: 'closed' }); root.innerHTML = '<div class="inside-component">My Component</div>'; }` A local variable preserves access for component setup while leaving the standard `shadowRoot` property unavailable to outside code. Storing that root on a public property would undermine the boundary. section 8.2
Closed mode is therefore an option for DOM encapsulation, not a complete security barrier. An open shadow root is presented as the more practical convention when controlled inspection or emergency access matters. section 8.4
