code: def parse_value(self, stream):
          
          if self.has_sequence(stream):
              value = self.parse_sequence(stream)
          elif self.has_set(stream):
              value = self.parse_set(stream)
          else:
              value = self.parse_simple_value(stream)
  
          self.skip_whitespace_or_comment(stream)
  
          if self.has_units(stream):
              return Units(value, self.parse_units(stream))
  
          return value
docs: Value ::= (SimpleValue | Set | Sequence) WSC UnitsExpression?