While the (safely composable) DOM with shadow trees provide the technical basis for defining web components, it does neither defines the concept of web components nor specifies the safety properties that web components should guarantee. Consequently, the standard also does not discuss how or even if the methods for modifying the DOM respect component boundaries. In AFP entry, we present a formally verified model of safely composable web components and define safety properties which ensure that different web components can only interact with each other using well-defined interfaces. Moreover, our verification of the application programming interface (API) of the DOM revealed numerous invariants that implementations of the DOM API need to preserve to ensure the integrity of components. In comparison to the strict standard compliance formalization of Web Components in the AFP entry "DOM_Components", the notion of components in this entry (based on "SC_DOM" and "Shadow_SC_DOM") provides much stronger safety guarantees.