Introduction to HTML Components
Personally, I think there's an important lesson here, and its the same lesson that polymer is learning as it stumbles around trying to convince people to use it.Most people don't actually derive much benefit from writing custom UI widget primitives.Certainly, that's a useful thing for a UI toolkit builder to be able to do, but tangibly, for most people, it's not actually useful.I don't have time to invest hours implementing `ImageDropDownSpinner` as a custom element.  is good enough for me, and heck, maybe I'll use some 3rd party widget if I need something special.That's not why react, vue, angular, etc. are winning the mind share of 'how to build web apps'; building UI widget is far less interesting than the ability to decompose your UI into a custom hierarchy of re-usable self contained units of functionality, that only at the lowest level actually involve UI components, is extremely powerful.They might look like custom widgets, but  isn't a UI widget, it's your entire application; that's the difference.It's easy to say this was a revolutionary idea, before its time, and it would have flown today instead of vanished into obscurity... but I think it missed the mark; it didn't solve problems people were actually having....but to be fair, it's easy to look at 'Web Component' efforts (like Polymer...) and go... yeah, this seems very familiar...