docs: def blob_handler(self, cmd):
          """Process a BlobCommand."""
          self.cmd_counts[cmd.name] += 1
          if cmd.mark is None:
              self.blobs['unmarked'].add(cmd.id)
          else:
              self.blobs['new'].add(cmd.id)
              # Marks can be re-used so remove it from used if already there.
              # Note: we definitely do NOT want to remove it from multi if
              # it's already in that set.
              try:
                  self.blobs['used'].remove(cmd.id)
              except KeyError:
                  pass