Salvo explains roof as a complete system, where underlayment, flashing, ventilation

https://andyodbz601.iamarrows.com/synthetic-roofing-roofing-shingles-that-resist-breaking-curling-and-moisture-damages

Salvo defines roofing as a full system, where underlayment, flashing, ventilation, and attaching must collaborate for trustworthy performance.