On the standards track: Yes
Is Experimental: No
Is Deprecated: No
In Chrome version 124 on 2024-04-16
In Chrome Android version 124 on 2024-04-16
In Edge version 124 on 2024-04-18
In Firefox version 123 on 2024-02-20
In Firefox for Android version 123 on 2024-02-20
Not in Internet Explorer
Not in Quest Browser
In Opera version 110 on 2024-05-14
In Opera Android version 82 on 2024-05-02
In Safari version 26 on 2025-09-15 Note: If there are custom elements in a declarative shadow root in the parsed HTML, then the elements' constructors and connectedCallback() methods are not called (bug 296420).
In Safari on iOS version 26 on 2025-09-15 Note: If there are custom elements in a declarative shadow root in the parsed HTML, then the elements' constructors and connectedCallback() methods are not called (bug 296420).
In Samsung Internet version 27.0 on 2024-11-06
In WebView Android version 124 on 2024-04-16
In WebView on iOS version 26 on 2025-09-15 Note: If there are custom elements in a declarative shadow root in the parsed HTML, then the elements' constructors and connectedCallback() methods are not called (bug 296420).