What exactly is infrastructure? Seeing the leopard's spots

We ducked a fundamental question raised by our proposal for infrastructure principles: “what exactly counts as infrastructure?” Of course this is not a straightforward question and part of the reason for leaving it in untouched in the introductory post. We believe that any definition must entail a much broader discussion from the community. But we wanted to kick this off with a discussion of an important part of the infrastructure puzzle that we think is often missed. That the infrastructure we should care most about is often a layer below where our attention is focused.