code: def _is_valid_value(self):
          
  
          comp_str = self._encoded_value
  
          value_pattern = []
          value_pattern.append("^((")
          value_pattern.append("~[")
          value_pattern.append(CPEComponent1_1._STRING)
          value_pattern.append("]+")
          value_pattern.append(")|(")
          value_pattern.append("[")
          value_pattern.append(CPEComponent1_1._STRING)
          value_pattern.append("]+(![")
          value_pattern.append(CPEComponent1_1._STRING)
          value_pattern.append("]+)*")
          value_pattern.append("))$")
  
          value_rxc = re.compile("".join(value_pattern))
          return value_rxc.match(comp_str) is not None
docs: Return True if the value of component in generic attribute is valid,
          and otherwise False.
  
          :returns: True if value is valid, False otherwise
          :rtype: boolean