184.108.40.206.3.1 Varying Strings
NDR64 represents a varying string as an ordered sequence of representations of the string elements preceded by two unsigned 64-bit integers. The first 64-bit integer MUST specify the offset from the first index of the string to the first index of the actual subset being passed. The second 64-bit integer MUST specify the actual number of elements being passed, including the terminator.
The first 64-bit integer (offset) MUST be 0 (zero). See the following figure.
Figure 9: Varying strings