5.2.6 Structures with optional fields
Structures with optional fields are encoded with an encoding mask and as a sequence of fields in the order that they appear in the definition. The encoding for each field is determined by the data type for the field.
The EncodingMask is a 32-bit unsigned integer. Each optional field is assigned exactly one bit, however, a single bit may control multiple fields. The bits assigned to fields may not be contiguous. Unassigned bits are set to 0 by encoders. Decoders shall report an error if assigned bits are not 0.

The part 'however, a single bit may control multiple fields' makes no sense.

It may be possible to define this with the OPC Binary schema but it cannot be defined through the UANodeset XML schema (which should be the leading schema) and also not possible with the new StructureField provided in the new DataTypeDescripiton attribute.

The part of the sentence should be removed from the spec, including an errata for 1.03.