Read and write property identifying to which Namespace this Identifier refers. This index must be between 0 (zero) and the number of Namespaces minus 1 (one) in the server. When defining a field in a Query, the index refers to the OPC UA Namespaces Collection defined in the Query object (which at some point may be different from the server's Namespaces Collection). Its value cannot be greater than 65535, because the OPC UA standard defines this is a 16-bit value.