The retailer is about to unveil a “sustainability index” on every product it sells.

Wal-Mart declined to discuss the index in advance of its meeting. So did other retailers. But details are trickling out.

"Bringing clarity to this question of what is more sustainable is a key role for Wal-Mart," said Rand Waddoups, senior director of business strategy and sustainability at Wal-Mart, when we talked at a Greenbiz.com conference in May.

"Imagine one day when every product on the shelf has behind it enough information from a life-cycle-thinking perspective that allows us to be much, much more intelligent about how we're buying," he went on. "And really, in the end, eventually, what consumers should be."

While Waddoups did not say much more than that, he made clear that one goal of the index will be to help consumers navigate conflicting or misleading claims.

"We understand green-washing. [Our customer] doesn't. She may not even be aware that it's going on," he said.

The initiative raises a thicket of questions, some about the very idea of a sustainability index and others about the nitty-gritty of its execution. To begin with, an obvious question: Who chose Wal-Mart to be America's regulator?