Enhanced UI is an overlay layer that uses native widgets on top of the basic Touch Orbiter to liven up the user experience. Traditionally, all Proxy_Orbiter based devices displayed a static image. Enhanced UI isn't a radical replacement for that. In fact, nothing was stripped out of the traditional behaviour. The overlay layer goes on top of that.
Proxy_Orbiter has been extended to generate XML descriptions for the Orbiter screen and Datagrid contents, which the overlay engine of a Enhanced UI capable device can interpret and create a native widget overlay.
This overlay doesn't have to be a one to one match to the description. For example, TouchOrbiterQt and Dianemo iOS Orbiter display only one grid in the media browser instead of the two that are in the screen. Also, to work around certain problems in the Proxy_Orbiter, the data is taken from the _MediaFile grid, but the touches are send as if the MediaFile (without the leading underscore) grid was touched, even though this grid isn't even made available to the user. The Proxy_Orbier isn't aware of the local layout.
Potential for extension:
Right now, the existing implementations only overlay native table widgets over the classic orbiter image and everything else works in the traditional way. Applications could make use of the rest of the information in the XML descriptions to add animation, special effects, and the like, to the overlay.