BLE/GattCharacteristic: Add explanatory note for a parameter

features/FEATURE_BLE/ble/GattCharacteristic.h

@@ -321,6 +321,11 @@ public:
      *        for the value attribute of a characteristic, then that particular
      *        characteristic may be considered optional and dropped while
      *        instantiating the service with the underlying BLE stack.
+     *
+     * @note  A CCCD should not be allocated if either the notify or indicate
+     *        flag is set, as it is handled by the underlying BLE stack. In such
+     *        a case, the param descriptors could be empty and the param
+     *        numDescriptors equal to zero.
      */
     GattCharacteristic(const UUID    &uuid,
                        uint8_t       *valuePtr       = NULL,
@@ -584,6 +589,8 @@ private:
     SecurityManager::SecurityMode_t   _requiredSecurity;
     /**
      * The characteristic's descriptor attributes.
+     * This contains only CCCDs that has neither the notify nor the indicate
+     * flag set, as thoses are handled by the underlying BLE stack.
      */
     GattAttribute                   **_descriptors;
     /**