What exactly is an IETM Level 4

Every few weeks someone in program office asks me the same question, usually with a slightly worried look: "Should we go for JSG 0852 or S1000D for our Level 4 IETM?" And almost every time, the worry is misplaced. They think they're choosing between "old" and "new," or "Indian" and "international," or "cheap" and "premium." That framing is exactly how projects end up with the wrong standard, a blown budget, and a deliverable nobody can actually open. So let's clear the fog. I