code: def parse(cls, parser, text, pos):
          
          found = False
  
          # Attempt to parse date specifier
          match = cls.date_specifiers_regex.match(text)
          if match:
              remaining_text, token, found = text[len(match.group(0)):], match.group(0), True
          else:
              # Attempt to parse arxiv identifier
              match = cls.arxiv_token_regex.match(text)
              if match:
                  remaining_text, token, found = text[len(match.group()):], match.group(2), True
              else:
                  # Attempt to parse a terminal token
                  remaining_text, token = SimpleValueUnit.parse_terminal_token(parser, text)
                  if type(token) != SyntaxError:
                      found = True
                  else:
                      # Attempt to parse a terminal with parentheses
                      try:
                          # Enable parsing a parenthesized terminal so that we can accept {+, -, |} as terminals.
                          parser._parsing_parenthesized_terminal = True
                          remaining_text, token = parser.parse(text, cls.parenthesized_token_grammar, pos)
  
                          found = True
                      except SyntaxError:
                          pass
                      except GrammarValueError:
                          raise
                      except ValueError:
                          pass
                      finally:
                          parser._parsing_parenthesized_terminal = False
  
          if found:
              result = remaining_text, SimpleValueUnit(token)
          else:
              result = text, SyntaxError("expecting match on " + cls.__name__)
  
          return result
docs: Imitates parsing a list grammar.
  
          Specifically, this
          grammar = [
              SimpleValueUnit.date_specifiers_regex,
              SimpleValueUnit.arxiv_token_regex,
              SimpleValueUnit.token_regex,
              SimpleValueUnit.parenthesized_token_grammar
          ].
  
          Parses plaintext which matches date specifiers or arxiv_identifier syntax, or is comprised of either 1) simple
          terminal (no parentheses) or 2) a parenthesized SimpleValue.
  
          For example, "e(+)" will be parsed in two steps, first, "e" token will be recognized and then "(+)", as a
          parenthesized SimpleValue.