roModel
From SAP Enable Now Wiki
Scope
Web Assistant parameter, specified either in the URL or in the Web Assistant parameters in the linked application.
Purpose
Not entirely sure. The only documentation I can find on it is that it should be set to "UACP or WPB depending on EXT mode", which doesn't exactly clear things up. in my testing it is necessary to have this set to UACP if you have the serviceLayerVersion set to EXT, or you won't see the SAP standard help content.
Usage
Specified as:
roModel=[null|UACP|WPB]