Extend Paper UI

Is it possible to extend the Paper UI administration UI like it is possible to extend OpenHAB generally with Addons. Or can I integrate other UIs beside PaperUI and HABPanel into OpenHAB.

I want to integrate external system as administrative UI into OpenHAB 2. Is that possible?

How is Habmin integrating with OpenHAB. Is this a completelly separate application or does the UI integrates in OpenHAB application?

I believe all the UIs including PaperUI and Habmin interact with OH itself through the REST API. But even if it doesn’t the UIs are an addon just like any other and there is an API it uses. Habmin is an add-on just like PaperUI and HABPanel and it is not a separate application.

However, the openHAB phone apps ARE separate applications and there are other UIs that are implemented as separate applications as well so that is an option too.