I think your workaround is probably the most preferable of the options. I've worked with mutation observers a lot and I wouldn't want to rely on them for anythi

I think your workaround is probably the most preferable of the options. I've worked with mutation observers a lot and I wouldn't want to rely on them for anything that didn't have a simpler mechanism to achieve the same thing. In "regular" frameworks, this problem would be expressed as state that is owned by A, that B's contribute to. Maybe by calling a function passed down to them, or by updating a shared store. It's a big shortcoming that composition of web components is limited to string attributes unless you use some sort of framework to mediate things.