code: def valid_hash_value(hashname):
      
      custom_hash_prefix_re = re.compile(r"^x_")
      if hashname in enums.HASH_ALGO_OV or custom_hash_prefix_re.match(hashname):
          return True
      else:
          return False
docs: Return true if given value is a valid, recommended hash name according
      to the STIX 2 specification.