docs: def valid_conkey(self, conkey):
          """Check that the conkey is a valid one. Return True if valid. A
          condition key is valid if it is one in the _COND_PREFIXES
          list. With the prefix removed, the remaining string must be
          either a number or the empty string."""
  
          for prefix in _COND_PREFIXES:
              trailing = conkey.lstrip(prefix)
              if trailing == '' and conkey:  # conkey is not empty
                  return True
              try:
                  int(trailing)
                  return True
              except ValueError:
                  pass
  
          return False