docs: def validate_tag(key, value):
      """Validate a tag.
  
      Keys must be less than 128 chars and values must be less than 256 chars.
      """
      # Note, parse_sql does not include a keys if the value is an empty string
      # (e.g. 'key=&test=a'), and thus technically we should not get strings
      # which have zero length.
      klen = len(key)
      vlen = len(value)
  
      return klen > 0 and klen < 256 and vlen > 0 and vlen < 256