code: def pop_refs(self, *refs):
          
          for ref in refs:
              name = ref.name
              count = self.counts[name]
              # Not tracking this ref
              if count < 1:
                  continue
              # Someone else is using this ref
              elif count > 1:
                  self.counts[name] -= 1
              # Last reference
              else:
                  logger.debug("popping last usage of {}".format(ref))
                  self.counts[name] -= 1
                  if ref.type == "value":
                      del self.attr_values[name]
                  else:
                      # Clean up both name indexes
                      path_segment = self.attr_names[name]
                      del self.attr_names[name]
                      del self.name_attr_index[path_segment]
docs: Decrement the usage of each ref by 1.
  
          If this was the last use of a ref, remove it from attr_names or attr_values.