code: def extract_fields(cls, schema):
          
          # -- BASED-ON: parse.Parser._generate_expression()
          for part in parse.PARSE_RE.split(schema):
              if not part or part == '{{' or part == '}}':
                  continue
              elif part[0] == '{':
                  # this will be a braces-delimited field to handle
                  yield cls.parse(part)
docs: Extract fields in a parse expression schema.
  
          :param schema: Parse expression schema/format to use (as string).
          :return: Generator for fields in schema (as Field objects).