[
  {"op": "doc", "text": "ref by a label that was never registered"},
  {"op": "source", "role": "price", "kind": "F64"},
  {"op": "use", "ref": {"name": "nope"}, "name": "sp"},
  {"op": "feed", "role": "price", "into": ["sp.price"]},
  {"op": "expose", "from": "sp.spread", "as": "spread"}
]