Interoperable: You can build a Web Component once and it should work "out of the box" in the latest Angular, React, Vue, Svelte, etc. (React was among the last holdouts on Web Component support because of Virtual DOM silliness.) Interoperable Web Components get us away from the era of needing to build npm libraries like ng-mycomponent, react-mycomponent, vue-mycomponent, for all the various combinations of drastically different component systems and ways of writing components, even when your component's core was as Vanilla as you could make it and you shared as much code as you could between implementations there were still so many small subtle things to do differently.