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 [now SEN] 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|SEN]
It is also possible to use a value of WPB, which has the same effect as SEN, but that value is being deprecated (as of Web Assistant 3.0.1) in favor of SEN.