Fiori Elements
What it is
A framework that generates a complete SAPUI5 Fiori app (list report, object page, etc.) from an OData service and its CDS @UI annotations — no hand-written UI code for the standard floorplans.
Why it matters for Clean Core
RAP + Fiori Elements is the Clean Core full-stack: model a business object, annotate it, and get a polished, consistent Fiori app for free. It's why CDS annotations matter so much.
Common pitfall
Dropping to freestyle SAPUI5 the moment something feels custom. Fiori Elements covers far more than people expect via annotations and extension points — exhaust those before hand-coding a UI you'll have to maintain.