code: public function getBooleanAttribute($strName, $blnDefault = false)
      {
          $strValue = $this->getAttribute($strName, $blnDefault ? 'true' : 'false');
          if (!in_array($strValue, array('true', 'false'))) {
              throw new Exception(
                  'Boolean attribute illegal value: "' . $strValue . '" valid values are "true" or "false"'
              );
          } else {
              return (($strValue == 'true') ? true : false);
          }
      }
docs: Get a boolean attribute value (value must either be 'true' or 'false')
  @param $strName
  @param bool $blnDefault
  @throws Exception
  @return bool