+ * @brief Const operator to access element with the specified index key.
+ *
+ * @SINCE_1_1.39
+ * @param[in] key The key whose value to access.
+ *
+ * @return The value for the element with the specified key, if key doesn't exist, then Property::NONE is returned.
+ *
+ * @note Will assert if invalid-key is given.
+ */
+ const Value& operator[]( Property::Index key ) const;
+
+ /**
+ * @brief Operator to access the element with the specified index key.
+ *
+ * @SINCE_1_1.39
+ * @param[in] key The key whose value to access.
+ *
+ * @return A reference to the value for the element with the specified key.
+ *
+ * @note If an element with the key does not exist, then it is created.
+ */
+ Value& operator[]( Property::Index key );
+
+ /**