I don't really agree that frontend framework components are meant to be replaced completely and are not composable. Maybe from the outside, but I use slots quit

I don't really agree that frontend framework components are meant to be replaced completely and are not composable. Maybe from the outside, but I use slots quite a lot in my components because they are very easy to do and they trivially work. Web Components on the other hand are usually demonstrated as insert <img-editor></img-editor> which basically inserts a ton of code to create some kind of an editor. Using slots in Web Components is a pain, a lot of appending nodes manually, templates as strings, for some more complicated things when I tried them I had to listen to the slotchange event etc. It's essentially the DOM api, which if it wasn't terrible, we wouldn't have switched to frontend frameworks like react etc. Also disagree with the side note that XHTML failed because it didn't augment HTML. IMHO it failed because if forced the applications to be completely valid and it put the validation on the client/browser. If you'd really used real XHTML a small error in the markup would've crashed your page. So we all validated our XHTML to be future ready, but it was always utopia that a business would risk crashing their, well, business because a p tag was not properly closed.