docs: def suck_out_editions(reporters):
      """Builds a dictionary mapping edition keys to their root name.
  
      The dictionary takes the form of:
          {
           "A.":   "A.",
           "A.2d": "A.",
           "A.3d": "A.",
           "A.D.": "A.D.",
           ...
          }
  
      In other words, this lets you go from an edition match to its parent key.
      """
      editions_out = {}
      for reporter_key, data_list in reporters.items():
          # For each reporter key...
          for data in data_list:
              # For each book it maps to...
              for edition_key, edition_value in data["editions"].items():
                  try:
                      editions_out[edition_key]
                  except KeyError:
                      # The item wasn't there; add it.
                      editions_out[edition_key] = reporter_key
      return editions_out