message: Add an example of accessing the impl storage to the 'DefiningAttributesAndTypes' document.
diff: @@ -232,6 +232,18 @@ public:
  }
  return success();
  }
  +
  + /// Return the parameter value.
  + unsigned getParameter() {
  + // 'getImpl' returns a pointer to our internal storage instance.
  + return getImpl()->nonZeroParam;
  + }
  +
  + /// Return the integer parameter type.
  + IntegerType getParameterType() {
  + // 'getImpl' returns a pointer to our internal storage instance.
  + return getImpl()->integerType;
  + }
  };
  ```
  